prepare repo for community maintenance

[SethTisue]

we'll need to expand the readme to include material similar to other module repos explaining that the module is community maintained, saying that maintainers are sought, explaining the 2.13 collections situation, etc.

once that's done we should do publicity via Discourse, Twitter, Gitter, etc and hope some interested maintainers emerge

[SethTisue]

docs for prospective maintainers don't especially exist, but they sort of nebulously meta-exist at scala/sbt-scala-module#16

[SethTisue]

we get so few issues opened in this repo that finding community maintainers has never become a priority

hopefully the lack of bug reports indicates that the quality is actually high, but it might be more that the number of users is low.... or some of both? it's hard to know.

[SethTisue]

not too long ago I changed the readme to say:

Maintenance status

This module is community-maintained, under the guidance of the Scala team at Lightbend. If you are
interested in participating, please jump right in on issues and pull
requests.

re: publicity, we'll do a bit of publicity around the 1.0.0 release, but I don't currently think much is needed.

as an aside, I've been mulling over writing a "State of the Scala Modules" blog post — it could be an annual series, where we run through the modules and say what's new and where things stand with each one.

anyway, I don't think we need to leave this ticket open any longer.