Need better documentation of all the things!

This includes better documentation for the following subjects:
* Setting up a basic environment for web development.
* Setting up a basic environment for developing core lightning plugins.
* Using the spawn command to spin up entire networks at once (similar to docker-compose)
* Using devmode to actively develop the codebase.
* Common tips and tricks for navigating and using the workbench.

Lot's of work to do!

No files, tests, or documentation entry points are named. Start by locating the existing documentation and the commands or entry points for environment setup, spawn, devmode, and workbench usage; the work is done when all five listed subjects have clear, usable guidance.

Written by the indexing model from the issue text.