contributing: add note on hotfixes [ci skip]
contributing: add note on hotfixes [ci skip]

ngzax/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,jfranklin9000/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,jfranklin9000/urbit,jfranklin9000/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,jfranklin9000/urbit,urbit/urbit,ngzax/urbit,jfranklin9000/urbit,urbit/urbit,jfranklin9000/urbit,jfranklin9000/urbit