Create a Netlify form for joining the community

Netlify forms can be used to let people 'become a developer' from their web browser. It allows signing using GitHub, for authenticated collection of their username to be added to the org. We could also add a field for the issue they want to be assigned to.

It is then easy for maintainers to invite them to the org after some rudimentary checks, or add a http://webtask.io which automatically invites them if they pass some basic automated checks to prevent abuse.

Probably a good app name is '/join'