Update README.md

README.md

@@ -11,6 +11,16 @@ Here is where you can find the source code for various parts of the Quarto syste
 
 - [Quarto VS Code Extension](https://github.com/quarto-dev/quarto/tree/main/apps/vscode)
 
+## Development
+
+To develop the Quarto VS Code extension, clone this repo, run `yarn`, then run the `yarn dev-vscode` command:
+
+```bash
+yarn             # install dependencies
+yarn dev-vscode  # run development/debug version of extension
+```
+
+Use the VS Code **Run and Debug** pane in the activity bar to run a version of VS Code with the development build of the extension.