Extend development guide

Scavenge information from a fresh extension's quickstart document and
put it into Development.md.

Fixes: VSCODEEXT-37
Change-Id: Ie8d4d8d5ff1c6ef63b10daa03b41e2b9e2148b54
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

Development.md

@@ -1,10 +1,17 @@
 # Development Guide
 
-## Build
+## Build on the command line
 
 - To install dependencies, run `npm ci`
 - To compile, run `npm run compile`
 
+## Running the extension from VS Code
+
+* Press `F5` to open a new window with your extension loaded.
+* You can relaunch the extension from the debug toolbar after changing code.
+* You can also reload (`Ctrl+R` or `Cmd+R` on Mac) the VS Code window with your extension to load
+  your changes.
+
 ## Pre-Commit
 
 Before every commit, the following commands should be run:
@@ -27,12 +34,25 @@ build together, run `npm run pretest`
 
 - To install the package to vscode, run `code --install-extension <vsix file generated in the previous step>`
 
-## Testing
+## Run tests on the command line
 
 - To run unit tests, run `npm run unitTests`
 - To run integration tests, run `npm run integrationTests -- --qt_path="<qt_installation>"`
 - To run all tests, run `npm run allTests -- --qt_path="<qt_installation>"`
 
+## Run tests from Visual Studio Code
+
+* Open the debug viewlet (`Ctrl+Shift+D` or `Cmd+Shift+D` on Mac) and from the launch configuration
+  dropdown pick `Extension Tests`.
+* Press `F5` to run the tests in a new window with your extension loaded.
+* See the output of the test result in the debug console.
+
+## Further reading
+
+* Explore the VS Code API by inspecting the file`node_modules/@types/vscode/index.d.ts`.
+* [Follow UX guidelines](https://code.visualstudio.com/api/ux-guidelines/overview) to create
+  extensions that seamlessly integrate with VS Code's native interface and patterns.
+
 ## Dependencies
 
 - [npm](https://www.npmjs.com/)