README: mysql/database: Added hint that backup is included

README.md

@@ -35,7 +35,7 @@ Following roles have been defined for making a server configuration easy:
 - **mysql** defines roles for handling mysql databases and users, uses *MariaDB*
   - **application** installs the main application with automatic backup
   - **backup_database** configures auto backup for a given mysql database
-  - **database** configures a database for an external application with its own user
+  - **database** configures a database for an external application with its own user (uses **mysql/backup_database**)
 - **nginx** defines roles to set up virtual servers, certificates will be requested by default
   - **application** installs and configures the main requirements
   - **forward** sets up a forwarding from one domain to another