Adding contact e-mail addresses to letsencrypt accounts via dehydrated / 2020-03-03

I noticed the news about LetsEncrypt revoking a lot of certificates on 4 March 2020 and did some checking to find out eventually that one of my certificates is in that set. Users have been notified of this problem... when their account had a contact e-mail address. By default dehydrated doesn't set an e-mail address so none of my instances used one. I do like to get informed so I searched how to update the contact info. The data is in /etc/dehydrated/config field CONTACT_EMAIL but I needed some searching before I found the method to get the update passed on to LetsEncrypt.

Some searching later found Update registration email address - Issue #425 dehydrated which shows that a simple dehydrated --account does the magic.