Add a walkthrough for first time users of the extension

[rbenegal]

Is your feature request related to a problem? Please describe.
Right now there isn’t a whole lot of guidance on how to use the Swift extension for VS Code once it is installed. Apart from reading an article about it and the “Details” tab of the Swift extension in VS Code it’s up to the user to realize that a Swift toolchain will have to be installed and figure out the workflow to Build, Run, Test and Debug code. As well, people who are installing the extension could be new to programming and Swift in general. A tutorial mode that will show the features of the extension will be greatly beneficial for first time users.

Describe the solution you'd like
The feature can possibly be implemented with VS Code Walkthrough mode or something similar to the CodeTour extension.

Expected outcomes/benefits

• A better onboarding experience for first time users of the VS Code Swift extension
• Users learn about the features of the extension