add a non-pull-request signing option

[Digit]

For those of us too technically inept to fathom how to do a pull request, or unwilling to directly use m$github,
please add an email address
for us to send our signatures of support to.

Please try lower the entry bar for the RMS support letter, to at least par with the attack letter.

[ais]

See #837.

It's not email, but it's something.