please provide documentation on how to develop the extension itself

[doudou]

I wanted to make a minor addition to the extension, but did not manage to test it.

I've tried the npm install route, but then I get an error on server start,

Cannot find module ./spinner

I'm really not familiar with the javascript packaging tools - I know just enough typescript/javascript to handle development.

[castwide]

The easiest way to test an extension under development is to run it from VS Code's debugger. This repo includes a "Launch Extension" configuration in the launch.json file. More information: https://code.visualstudio.com/api/get-started/your-first-extension

If you're trying to install a local build of the extension, you probably need to run npm run compile first.