update docs content (#11374)

Move all docs to zed repo

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>
Co-authored-by: Marshall <marshall@zed.dev>

docs/README.md

@@ -0,0 +1,14 @@
+Welcome to Zed's documentation.
+
+This is built on push to `main` and published automatically to [https://zed.dev/docs](https://zed.dev/docs).
+
+To preview the docs locally you will need to install [mdBook](https://rust-lang.github.io/mdBook/), and then run:
+
+```
+mdbook serve docs
+```
+
+### Internal docs:
+
+- We have a Cloudflare router called `docs-proxy`that intercepts requests to `zed.dev/docs` and forwards them to the "docs" Cloudflare Pages project.
+- CI uploads a new version to the Pages project from `.github/workflows/deploy_docs.yml` on every push to `main`.