Add admonition about CIVS invalid domains

[proofconstruction]

When trying to activate my email on the CIVS voting platform, I received the error "Illegal mail address". I tested with a few other domains, and found that the site simply won't accept several valid ones.

This PR updates the README with an admonition warning about this possibility.

[infinisil]

Oh damn. I guess let's have something like this for now, but I'll think about adding a check for that. In particular, we can see the regex that is used to check this in the source

[infinisil]

I opened andrewcmyers/civs#61 to increase the maximum allowed TLD length. Furthermore I created a script to check whether an Email address would be invalid for CIVS, but running it over all Emails, it only found two:

$ scripts/check-mail.pl < $(nix-build -A voters)/emails.txt
"^"@regexmail.net
[email protected]

The first one I believe is an actually invalid email (also failed to send), but the only other email is yours, so I don't think we need to put this as a warning.

Unless the PR gets merged and deployed soon, could you register an alternate email address instead?

[proofconstruction]

The first one I believe is an actually invalid email (also #1), but the only other email is yours, so I don't think we need to put this as a warning.

Up to you! I updated the commit in this PR to move this admonition to email.md, in any case.

Unless the PR gets merged and deployed soon, could you register an alternate email address instead?

Done in #33

[ryantrinkle]

The first one I believe is an actually invalid email (also failed to send)

I actually think it's valid - the "local part" of an email address is almost absurdly flexible; see https://en.wikipedia.org/wiki/Email_address#Local-part

[infinisil]

Let's close this, thanks for pointing this out in any case!