Document process for access control to Typelevel repositories  #324

Ref https://gitter.im/typelevel/general?at=57222f544cd0ac7a27ed46a2

Summary:

"For bintray, ie sbt-catalysts, currently on @milessabin @larsrh and myself have access there. Technically, this enough, but I feel at least one extra is needed to do releases.
Any thoughts..? ref https://bintray.com/typelevel

This is a job for a typelevel/general issue ... we need a list of people who currently have permissions (both Sonatype and Bintray) and the skeleton of a process for how someone gets on or off that list.

I have extended this to include Typelevel based github repositories too, as they are very much related.