📝 Update source code structure.

Author: zcbenz

docs/development/source-code-directory-structure.md

@@ -12,11 +12,10 @@ to understand the source code better.
 ## Structure of source code
 
 * **atom** - Source code of atom-shell.
-  * **app** - Contains system entry code, this is the most basic level of the
-    program.
+  * **app** - System entry code.
   * **browser** - The frontend including the main window, UI, and all browser
     side things. This talks to the renderer to manage web pages.
-    * **lib** - Javascript part of browser initialization code.
+    * **lib** - Javascript part of browser sidde initialization code.
     * **ui** - Implementation of UI stuff for different platforms.
       * **cocoa** - Cocoa specific source code.
       * **gtk** - GTK+ specific source code.
@@ -26,31 +25,38 @@ to understand the source code better.
     * **api** - The implementation of browser side APIs.
        * **lib** - Javascript part of the API implementation.
     * **net** - Network related code.
-  * **renderer** - Code that runs in renderer.
+    * **mac** - Mac specific Objective-C source code.
+    * **resources** - Icons, platform-dependent files, etc.
+  * **renderer** - Code that runs in renderer process.
     * **lib** - Javascript part of renderer initialization code.
     * **api** - The implementation of renderer side APIs.
        * **lib** - Javascript part of the API implementation.
   * **common** - Code that used by both browser and renderer, including some
-    utility functions and code to integrate node's message loop into Chromium's message loop.
+    utility functions and code to integrate node's message loop into Chromium's
+    message loop.
     * **lib** - Common Javascript initialization code.
-    * **v8** - Utility functions for using V8 and node APIs.
     * **api** - The implementation of common APIs, and foundations of
       atom-shell's built-in modules.
        * **lib** - Javascript part of the API implementation.
-  * **spec** - Automatic tests.
-  * **script** - Scripts for building atom-shell.
-* **chrome** - Source code modified from Chromium's chrome component.
+* **chrome** - Source code modified from Chromium's `chrome` component.
+* **docs** - Documentations.
+* **spec** - Automatic tests.
+* **atom.gyp** - Building rules of atom-shell.
+* **common.gypi** - Compiler specific settings and building rules for other
+  components like `node` and `breakpad`.
 
 ## Structure of other directories
 
-* **vendor** - Build dependencies.
-* **tools** - Helper scripts used by gyp files.
-* **node_modules** - Third party node modules used for building or running
-  specs.
-* **out** - Output directory for `ninja`.
+* **script** - Scripts used for development purpose like building, packaging,
+  testing, etc.
+* **tools** - Helper scripts used by gyp files, unlike `script`, scripts put
+  here should never be invoked by users directly.
+* **vendor** - Source code of third party dependencies, we didn't use
+  `third_party` as name because it would confuse with the same directory in
+  Chromium's source code tree.
+* **node_modules** - Third party node modules used for building.
+* **out** - Temporary output directory of `ninja`.
 * **dist** - Temporary directory created by `script/create-dist.py` script
   when creating an distribution.
-* **node** - Downloaded node binary, it's built from
-  https://github.com/atom/node/tree/chromium-v8.
-* **frameworks** - Downloaded third-party binaries of frameworks (only on
-  Mac).
+* **frameworks** - Downloaded binaries of third-party frameworks, binaries
+  here are usually either closed source or hard to be built via `gyp`.