Add CONTRIBUTING guide
Add CONTRIBUTING guide

jonathanstowe/panda,stmuk/panda,perlpilot/panda,niner/panda,hoelzro/panda,skaji/panda,niner/panda,perlpilot/panda,hoelzro/panda,sjn/panda,jonathanstowe/panda,will-crawford/panda,timo/panda,sjn/panda,shoichikaji/panda,hoelzro/panda,sjn/panda,will-crawford/panda,tadzik/panda,timo/panda,TimToady/panda,laben/panda,nbrown/panda,stmuk/panda,shoichikaji/panda,TimToady/panda,skaji/panda,tadzik/panda,laben/panda,moznion/panda,moznion/panda,nbrown/panda,tadzik/panda