[bug#57952] [PATCH] gnu: Add guix-send-email.

[Ludovic Courtès]

Hi!

I must say I’m a bit skeptical about the usefulness of the extension,
though it looks pretty fun :-) and also a good example of how to write
an extension (similar to what Simon presented in Paris).

Maybe we should just keep it as an example in the source tree?

Thanks,
Ludo’.