Instruct to stop the service only after git pulling and getting deps to minimize downtimes

docs/admin/updating.md

 # Updating your instance
-1. Stop the Pleroma service.
-2. Go to the working directory of Pleroma (default is `/opt/pleroma`)
-3. Run `git pull`. This pulls the latest changes from upstream.
-4. Run `mix deps.get`. This pulls in any new dependencies.
+1. Go to the working directory of Pleroma (default is `/opt/pleroma`)
+2. Run `git pull`. This pulls the latest changes from upstream.
+3. Run `mix deps.get`. This pulls in any new dependencies.
+4. Stop the Pleroma service.
 5. Run `mix ecto.migrate`[^1]. This task performs database migrations, if there were any.
 6. Restart the Pleroma service.