Software Packaging Guidelines
zorbash.com
zorbash.com
One thing I'd like to add: in your Readme, put information how you can find further documentation (and if it is in the same repo, how it is built). A surprising number of projects have some basic instructions in the readme, and then a /documentation folder or an external website, without any clear reference to it.
A common pattern out there, is projects keeping some documentation in their repo's wiki and not mentioning it in the Readme. Unfortunately GitHub does not provide a visual hint on how often a wiki is updated in the repo page.