All: Add CONTRIBUTING.md
All: Add CONTRIBUTING.md

cassos/mgba,sergiobenrocha2/mgba,libretro/mgba,iracigt/mgba,iracigt/mgba,Touched/mgba,cassos/mgba,cassos/mgba,Touched/mgba,mgba-emu/mgba,AdmiralCurtiss/mgba,askotx/mgba,Iniquitatis/mgba,askotx/mgba,mgba-emu/mgba,fr500/mgba,mgba-emu/mgba,zerofalcon/mgba,libretro/mgba,Anty-Lemon/mgba,Iniquitatis/mgba,AdmiralCurtiss/mgba,Iniquitatis/mgba,askotx/mgba,sergiobenrocha2/mgba,MerryMage/mgba,libretro/mgba,askotx/mgba,jeremyherbert/mgba,libretro/mgba,jeremyherbert/mgba,Anty-Lemon/mgba,fr500/mgba,AdmiralCurtiss/mgba,iracigt/mgba,Touched/mgba,libretro/mgba,fr500/mgba,bentley/mgba,fr500/mgba,Anty-Lemon/mgba,zerofalcon/mgba,zerofalcon/mgba,iracigt/mgba,Anty-Lemon/mgba,mgba-emu/mgba,Iniquitatis/mgba,jeremyherbert/mgba,sergiobenrocha2/mgba,bentley/mgba,jeremyherbert/mgba,sergiobenrocha2/mgba,MerryMage/mgba,matthewbauer/mgba,sergiobenrocha2/mgba,matthewbauer/mgba,MerryMage/mgba