Add self-hosting image update instructions

Author: nicktrn

docs/open-source-self-hosting.mdx

@@ -308,6 +308,7 @@ If you're coming from the beta CLI package images, you will need to:
 - **Switch branches.** We moved back to main. Run `git checkout main` in your docker repo.
 - **Pull in updates.** We've added a new container for [Electric](https://github.com/electric-sql/electric) and made some other improvements. Run `git pull` to get the latest updates.
 - **Apply your changes.** If you stashed your changes, apply them with `git stash pop`.
+- **Update your images.** We've also published new images. Run `./update.sh` to pull them.
 - **Restart all services.** Run `./stop.sh && ./start.sh` and you're good to go.
 
 In summary, run this wherever you cloned the docker repo:
@@ -323,7 +324,8 @@ git pull
 # if you stashed your changes
 git stash pop
 
-# restart your services
+# update and restart your services
+./update.sh
 ./stop.sh && ./start.sh
 ```