Deploy collab like nightly (#7174)

After this change we'll be able to push a tag to github to deploy to
collab.

The advantages of this are that there's no longer a separate step to
first
build the image, and then deploy it.

In the future I'd like to make this happen more automatically (maybe as
part of
bump nightly).

Release Notes:

- N/A

crates/collab/README.md

@@ -3,3 +3,35 @@
 This crate is what we run at https://collab.zed.dev.
 
 It contains our back-end logic for collaboration, to which we connect from the Zed client via a websocket after authenticating via https://zed.dev, which is a separate repo running on Vercel.
+
+# Local Development
+
+ Detailed instructions on getting started are [here](https://zed.dev/docs/local-collaboration).
+
+# Deployment
+
+We run two instances of collab:
+
+* Staging (https://staging-collab.zed.dev)
+* Production (https://collab.zed.dev)
+
+Both of these run on the Kubernetes cluster hosted in Digital Ocean.
+
+Deployment is triggered by pushing to the `collab-staging` (or `collab-production`) tag in Github. The best way to do this is:
+
+* `./script/deploy-collab staging`
+* `./script/deploy-collab production`
+
+You can tell what is currently deployed with `./script/what-is-deployed`.
+
+# Database Migrations
+
+To create a new migration:
+
+```
+./script/sqlx migrate add <name>
+```
+
+Migrations are run automatically on service start, so run `foreman start` again. The service will crash if the migrations fail.
+
+When you create a new migration, you also need to update the [SQLite schema](./migrations.sqlite/20221109000000_test_schema.sql) that is used for testing.