Improve development documentation

[kylecarbs]

There are essentially no docs related to developing or maintaining code-server.

Checklist:

• How to update the VS Code version (including patch updates) (manually and for CI).
• What does each bundle do?
• How does it work?
• How to build from source (including required dependencies).

[edwinbrowwn]

Hopefully this helps..
https://medium.com/@malikbrowwn/how-to-host-vs-code-on-a-vps-using-coder-aka-code-server-d519767fb52c