Rework README
Rework README

Promote Docker dev instructions and give warning to using manual dev instructions.
Remove broken waffle badge.
Remove text about using 5.x branch for Fedora 3 support.
uvalib/avalon,nulib/avalon,avalonmediasystem/avalon,avalonmediasystem/avalon,nulib/avalon,nulib/avalon,uvalib/avalon,uvalib/avalon,uvalib/avalon,avalonmediasystem/avalon,nulib/avalon,avalonmediasystem/avalon