Update databases.md

run mysql_secure_installation to secure the freshly installed mysql server

doc/install/databases.md

@@ -14,6 +14,9 @@ GitLab supports the following databases:
     # Pick a database root password (can be anything), type it and press enter
     # Retype the database root password and press enter
+    # Secure your installation.
+    sudo mysql_secure_installation
+    
     # Login to MySQL
     mysql -u root -p