`Documentation Fix: Add clear instructions for local dev environment setup`

Hello! While trying to contribute to the Jupyter Notebook project, I noticed the documentation for setting up a local development environment is a bit sparse and assumes prior experience.

Areas for Improvement:

The configuration for development dependencies (e.g., npm, node, Python 3.x) isn’t clearly defined.

No command example is shown for live-reloading during development (jupyter notebook --NotebookApp.allow_origin='*', etc.).

A troubleshooting section for dependency errors or build failures would help new contributors significantly.

Suggested Enhancements:

Add a brief “Setup for Development” subsection detailing required versions and install commands.

Include usage examples for launching notebook with dev flags.

Provide quick fixes for errors commonly encountered (e.g., missing build tools, failing JS builds).

I’d love to submit a PR if this improvement would be welcome!

Start by locating the contributor or development setup documentation and review the existing instructions. Add the requested dependency versions and install commands, notebook launch examples, and troubleshooting guidance; done means a new contributor can follow the setup and address common dependency or build failures.