message: add how to debug PDF viewer
diff: @@ -28,6 +28,10 @@ To build a release image, run
  npm run release
  -## Testing the extension
  +## Testing and debugging the extension
  In VS Code, simply press `<F5>` (or run `Debug: Start Debugging` from the command palette) and a new window will pop up where you can test the extension.
  +
  +### Debugging PDF viewer
  +
  +To debug the internal PDF viewer, select `View LaTeX PDF > View in web browser,` and view a PDF file in Google Chrome. You can debug the viewer with [Chrome DevTools](https://developers.google.com/web/tools/chrome-devtools/) as a general web application.
  