Update documentation to check postgre status

doc/install/installation.md

@@ -303,6 +303,13 @@ use of extensions and concurrent index removal, you need at least PostgreSQL 9.2
    sudo apt-get install -y postgresql postgresql-client libpq-dev postgresql-contrib
    ```
 
+1. Start the PostgreSQL service and confirm that the service is running:
+
+   ```shell
+   sudo service postgresql start
+   sudo service postgresql status
+   ```
+
 1. Create a database user for GitLab:
 
    ```shell