Improve gui/src/qt README.md

The current readme is a little bit outdated and contains some grammatical mistakes. This commit updates the doc so that:
  - It is easier to follow and is more informative
  - Fixes grammatical mistakes
  - Modernizes the Qt Creater setup instructions
  - Adds UNIX instructions for Qt Creator setup

Author: jarolrod

src/qt/README.md

@@ -1,95 +1,124 @@
-This directory contains the BitcoinQT graphical user interface (GUI). It uses the cross-platform framework [Qt](https://www1.qt.io/developers/).
+This directory contains the source code for the Bitcoin Core graphical user interface (GUI). It uses the [Qt](https://www1.qt.io/developers/) cross-platform framework.
 
 The current precise version for Qt 5 is specified in [qt.mk](/depends/packages/qt.mk).
 
 ## Compile and run
 
-See build instructions ([macOS](/doc/build-osx.md), [Windows](/doc/build-windows.md), [Unix](/doc/build-unix.md), etc).
+See build instructions: [Unix](/doc/build-unix.md), [macOS](/doc/build-osx.md), [Windows](/doc/build-windows.md), [FreeBSD](/doc/build-freebsd.md), [NetBSD](/doc/build-netbsd.md), [OpenBSD](/doc/build-openbsd.md)
+
+When following your systems build instructions, make sure to install the `Qt` dependencies.
 
 To run:
 
 ```sh
 ./src/qt/bitcoin-qt
 ```
 
-## Files and directories
-
-### forms
+## Files and Directories
 
-Contains [Designer UI](https://doc.qt.io/qt-5.9/designer-using-a-ui-file.html) files. They are created with [Qt Creator](#using-qt-creator-as-ide), but can be edited using any text editor.
+#### forms/
 
-### locale
+- A directory that contains [Designer UI](https://doc.qt.io/qt-5.9/designer-using-a-ui-file.html) files. These files specify the characteristics of form elements in XML. Qt UI files can be edited with [Qt Creator](#using-qt-creator-as-ide) or using any text editor.
 
-Contains translations. They are periodically updated. The process is described [here](/doc/translation_process.md).
+#### locale/
 
-### res
+- Contains translations. They are periodically updated and an effort is made to support as many languages as possible. The process of contributing translations is described in [doc/translation_process.md](/doc/translation_process.md).
 
-Resources such as the icon.
+#### res/
 
-### test
+ - Contains graphical resources used to enhance the UI experience.
 
-Tests.
+#### test/
 
-### bitcoingui.(h/cpp)
+- Functional tests used to ensure proper functionality of the GUI. Significant changes to the GUI code normally require new or updated tests.
 
-Represents the main window of the Bitcoin UI.
+#### bitcoingui.(h/cpp)
 
-### \*model.(h/cpp)
+- Represents the main window of the Bitcoin UI.
 
-The model. When it has a corresponding controller, it generally inherits from  [QAbstractTableModel](https://doc.qt.io/qt-5/qabstracttablemodel.html). Models that are used by controllers as helpers inherit from other Qt classes like [QValidator](https://doc.qt.io/qt-5/qvalidator.html).
+#### \*model.(h/cpp)
 
-ClientModel is used by the main application `bitcoingui` and several models like `peertablemodel`.
+- The model. When it has a corresponding controller, it generally inherits from  [QAbstractTableModel](https://doc.qt.io/qt-5/qabstracttablemodel.html). Models that are used by controllers as helpers inherit from other Qt classes like [QValidator](https://doc.qt.io/qt-5/qvalidator.html).
+- ClientModel is used by the main application `bitcoingui` and several models like `peertablemodel`.
 
-### \*page.(h/cpp)
+#### \*page.(h/cpp)
 
-A controller. `:NAMEpage.cpp` generally includes `:NAMEmodel.h` and `forms/:NAME.page.ui` with a similar `:NAME`.
+- A controller. `:NAMEpage.cpp` generally includes `:NAMEmodel.h` and `forms/:NAME.page.ui` with a similar `:NAME`.
 
-### \*dialog.(h/cpp)
+#### \*dialog.(h/cpp)
 
-Various dialogs, e.g. to open a URL. Inherit from [QDialog](https://doc.qt.io/qt-5/qdialog.html).
+- Various dialogs, e.g. to open a URL. Inherit from [QDialog](https://doc.qt.io/qt-5/qdialog.html).
 
-### paymentserver.(h/cpp)
+#### paymentserver.(h/cpp)
 
-Used to process BIP21 payment URI requests. Also handles URI based application switching (e.g. when following a bitcoin:... link from a browser).
+- (Deprecated) Used to process BIP21 payment URI requests. Also handles URI-based application switching (e.g. when following a bitcoin:... link from a browser).
 
-### walletview.(h/cpp)
+#### walletview.(h/cpp)
 
-Represents the view to a single wallet.
+- Represents the view to a single wallet.
 
-### Other .h/cpp files
+#### Other .h/cpp files
 
 * UI elements like BitcoinAmountField, which inherit from QWidget.
 * `bitcoinstrings.cpp`: automatically generated
-* `bitcoinunits.(h/cpp)`: BTC / mBTC / etc handling
+* `bitcoinunits.(h/cpp)`: BTC / mBTC / etc. handling
 * `callback.h`
-* `guiconstants.h`: UI colors, app name, etc
+* `guiconstants.h`: UI colors, app name, etc.
 * `guiutil.h`: several helper functions
 * `macdockiconhandler.(h/mm)`: macOS dock icon handler
 * `macnotificationhandler.(h/mm)`: display notifications in macOS
 
 ## Contribute
 
-See [CONTRIBUTING.md](/CONTRIBUTING.md) for general guidelines. Specifically for Qt:
+See [CONTRIBUTING.md](/CONTRIBUTING.md) for general guidelines.
+
+**Note:** Do not change `local/bitcoin_en.ts`. It is updated [automatically](/doc/translation_process.md#writing-code-with-translations).
+
+## Using Qt Creator as an IDE
+
+[Qt Creator](https://www.qt.io/product/development-tools) is a powerful tool which packages a UI designer tool (Qt Designer) and a C++ IDE into one application. This is especially useful if you want to change the UI layout.
+
+#### Download Qt Creator
+
+On Unix and macOS, Qt Creator can be installed through your package manager. Alternatively, you can download a binary from the [Qt Website](https://www.qt.io/download/).
+
+**Note:** If installing from a binary grabbed from the Qt Website: During the installation process, uncheck everything except for `Qt Creator`.
+
+##### macOS
+
+```sh
+brew install qt-creator
+```
+
+##### Ubuntu & Debian
+
+```sh
+sudo apt-get install qtcreator
+```
+
+#### Setup Qt Creator
 
-* don't change `local/bitcoin_en.ts`; this happens [automatically](/doc/translation_process.md#writing-code-with-translations)
+1. Make sure you've installed all dependencies specified in your systems build instructions
+2. Follow the compile instructions for your system, run `./configure` with the `--enable-debug` flag
+3. Start Qt Creator. At the start page, do: `New` -> `Import Project` -> `Import Existing Project`
+4. Enter `bitcoin-qt` as the Project Name and enter the absolute path to `src/qt` as Location
+5. Check over the file selection, you may need to select the `forms` directory (necessary if you intend to edit *.ui files)
+6. Confirm the `Summary` page
+7. In the `Projects` tab, select `Manage Kits...`
 
-## Using Qt Creator as IDE
+ **macOS**
+ - Under `Kits`: select the default "Desktop" kit
+ - Under `Compilers`: select `"Clang (x86 64bit in /usr/bin)"`
+ - Under `Debuggers`: select `"LLDB"` as debugger (you might need to set the path to your LLDB installation)
 
-You can use Qt Creator as an IDE. This is especially useful if you want to change
-the UI layout.
+ **Ubuntu & Debian**
 
-Download and install the community edition of [Qt Creator](https://www.qt.io/download/).
-Uncheck everything except Qt Creator during the installation process.
+ Note: Some of these options may already be set
 
-Instructions for macOS:
+ - Under `Kits`: select the default "Desktop" kit
+ - Under `Compilers`: select `"GCC (x86 64bit in /usr/bin)"`
+ - Under `Debuggers`: select `"GDB"` as debugger
 
-1. Make sure you installed everything through Homebrew mentioned in the [macOS build instructions](/doc/build-osx.md)
-2. Use `./configure` with the `--enable-debug` flag
-3. In Qt Creator do "New Project" -> Import Project -> Import Existing Project
-4. Enter "bitcoin-qt" as project name, enter src/qt as location
-5. Leave the file selection as it is
-6. Confirm the "summary page"
-7. In the "Projects" tab select "Manage Kits..."
-8. Select the default "Desktop" kit and select "Clang (x86 64bit in /usr/bin)" as compiler
-9. Select LLDB as debugger (you might need to set the path to your installation)
-10. Start debugging with Qt Creator (you might need to the executable to "bitcoin-qt" under "Run", which is where you can also add command line arguments)
+8. While in the `Projects` tab, ensure that you have the `bitcoin-qt` executable specified under `Run`
+ - If the executable is not specified: click `"Choose..."`, navigate to `src/qt`, and select `bitcoin-qt`
+9. You're all set! Start developing, building, and debugging the Bitcoin Core GUI