Who's using JMAP?

[chmac]

Would be great to add a list of "who's using JMAP" either to the site or somewhere here on GitHub. I'm assuming that folks besides FastMail are deploying it and it'd be great to see who they are to get a better sense of what adoption looks like.

[marclaporte]

See here: https://jmap.io/software.html

And some here: https://www.openhub.net/tags?names=jmap

[marclaporte]

#313