Add backup user in readme

Nautikos1235 · Nautikos1235 · commit 1308809028f3 · 2019-09-23T10:12:08.000+02:00
diff --git a/README.md b/README.md
@@ -146,6 +146,9 @@ mongodb_user_admin_password: passw0rd
 
 mongodb_root_admin_name: siteRootAdmin
 mongodb_root_admin_password: passw0rd
+
+mongodb_root_backup_name: backupuser
+mongodb_root_backup_password: passw0rd
 ```
 
 #### Usage
