Update README
Update README

add notice about frozen master branch
MiLk/hummingbird,Snitzle/hummingbird,astraldragon/hummingbird,vevix/hummingbird,Snitzle/hummingbird,Snitzle/hummingbird,jcoady9/hummingbird,astraldragon/hummingbird,jcoady9/hummingbird,MiLk/hummingbird,astraldragon/hummingbird,MiLk/hummingbird,vevix/hummingbird,MiLk/hummingbird,vevix/hummingbird,jcoady9/hummingbird,jcoady9/hummingbird,vevix/hummingbird,Snitzle/hummingbird,astraldragon/hummingbird