Warn staff about the consequences of resetting the calendar feed URL

Linked to case: PPLHR-I-435

After having the problem with our calendar feed URL and suggesting staff update their personal calendars, as per the correct instructions from your knowledge support page. I have since discovered that when somebody hits reset on the URL, it makes all staff who have previously set up their calendar feed no longer receive up to date information.

Surely you should put a warning on, so staff are aware and do not assume their data is up to date