Update docs for running collab locally (#23192)

Mention `cargo run -p collab -- serve all`, which seem to be the easier
way to run it.

Release Notes:

- N/A

docs/src/development/local-collaboration.md

@@ -33,10 +33,12 @@ To use a different set of admin users, you can create your own version of that j
 
 ## Testing collaborative features locally
 
-In one terminal, run Zed's collaboration server and the `livekit` dev server:
+Ensure that Postgres is configured and running, then run Zed's collaboration server and the `livekit` dev server:
 
 ```sh
 foreman start
+# OR
+cargo run -p collab -- serve all
 ```
 
 In a second terminal, run two or more instances of Zed.