Document executing commands from the dev tools console

[jtpio]

As discussed in #22.

So it's easier to test the commands while working on the extension.

[nakul-py]

@jtpio I think we can do this in Contributing.md instead of Readme

[nakul-py]

And one more thing can we add Contributing page link or one or two line description in Readme.

like

### Contributing
We welcome contributions from the community! To contribute:

- Fork the repository
- Make a development install of jupyterlab-diff
- Create a new branch
- Make your changes
- Submit a pull request
For more details, check out our [CONTRIBUTING.md](https://github.com/jupyter-ai-contrib/jupyterlab-diff?tab=contributing-ov-file).

[jtpio]

Thanks all!

@nakul-py would you to open a follow-up PR after this one with your suggestions?

[nakul-py]

Thanks all!

@nakul-py would you to open a follow-up PR after this one with your suggestions?

Ok Jeremy!