Add wordpress credentials instructions

web/wordpress.markdown

@@ -9,7 +9,10 @@ Please see [[general web share instructions|web/webshares]].
 Administration and customization
 --------------------------------
 
-Open `https://yourdomain.phys.ethz.ch/wp-admin/` in your browser.
+Open `https://yourdomain.phys.ethz.ch/wp-admin/` in your browser and use the credentials:
+
+- Username: `admin`
+- Password: use 'database_password' from `private/database.yml`
 
 Go to **Settings** > **General** and change **Administration Email Address** to your address.