The README seems good to me. It all makes sense despite me not having used GitHub and not understanding some of the terms. But, I feel confident from the README that I would be able to do what I was trying to do.
From a language point of view, this sentence is a bit weird and I'd split it into two:
The distmgr command line application that's installed along with the Dist::Mgr Perl distribution provides the facility to manage Perl distributions that you're the author of.
"The distmgr command line application that's installed along with the Dist::Mgr Perl distribution. It provides the facility to manage Perl distributions that you've authored."