[ANN] Announcing gemcert, a simple certificate generator

[colecmac at protonmail.com]

This looks great, thanks!

> Prefer ED25519

I know you mention this on the README, but I just want to remind people
that it's probably best to stick with EC keys for now, as not all clients
and servers support ed25519. And the size is similar.

Also, could you add a go.mod and go.sum file to your repo. You can easily
make one with `go mod init`, just make sure the path in go.mod is correct.
That would allow using go get on the repo.

Thanks,
makeworld