jco documentation effort

[guybedford]

Currently documentation for the project is very minimal. This includes both for using jco and contributing to jco (tracked in #62).

Thanks to @divya-mohan0209 for raising this topic more broadly, that while there is a "documentation" label currently tracking various minor issues, there is a need for a more general documentation effort for the project as it heads towards stabilization.

The first thing to note is that this project is effectively a monorepo, it covers several projects:

• preview2-shims for Node.js and the browser
• component transpilation workflows
• component typescript generation
• wasm-tools for JavaScript
• the bindgen crate
• a componentize wrapper

As a go-to tool, we should probably move towards having the more technical project-specific readmes in each of the individual project folders, while the main landing page readme should likely be high level as this tool is catered to a high level audience that "just wants to use components in js".

Therefore any documentation work I think should start from that premise, and create a simple journey through the workflows, before diving into the more technical materials. The main landing readme should discuss the various projects and explain them in context, while also pointing users int he right direction for what they likely need. Community links and reference material links should be available from the start.