[[PR Description]]

These docs are intended to replace both docs.zed.dev and introduce
people to how to build Zed from source.

Add or edit markdown files in the docs/src folder, and follow the
instructions in `how-to-deploy.md` to deploy the docs on
[Vercel](https://vercel.com/zed-industries/zed-app-docs/45ZTNBKSCmCMAvfAcfcocGnmoMyd).

Add pages and organize/reorder docs in the SUMMARY.md.

When you are sure a page is added or is no longer needed you can delete
it from `docs/old`

Release Notes:

- N/A