Create CONTRIBUTING.md

Simple file (which github will show for those making PRs) containing guidelines for making PRs.
Feel free to comment if you want/need anything added. I can pull the same thing to FML too if you'd like, Lex.
Update CONTRIBUTING.md

Add link to wiki page on contributing
Fixed biome weights not working with non multiples of 10
Prevent client only commands from bleeding through to the server.
Merge pull request #1219 from Lunatrius/master

Prevent client only commands from bleeding through to the server.
Disable by default the Display Stencil bits. Keep FBO bits. Acording to Mumfery and ChickenBones, it should not be nessasary and should solve the 1/4 main menu issue. Use -Dforge.forceDisplayStencil=true to enable old behavior.
MinecraftForge/FML@d00feb58c762b0bbc506d79faf1ce40bc96732e9 Remove debug code that was causing console spam in Forge.
Fix vanilla lighting issue and blending issues in achievements gui. Closes #1445
Merge pull request #1364 from Adubbz/master

Fixed biome weights not working with non multiples of 10
Fixed desert list initialization. Fixes #1447
Added PlayerWakeUpEvent
Merge pull request #1418 from Parker8283/wakeupevent

Added PlayerWakeUpEvent
Compleetly disable stencil bits unless told not to by using the -Dforge.forceDisplayStencil=true flag. Should solve the 'menu in bottom corner' issue with Intel Integrated graphics cards.
implemented crowdin support
Merge pull request #1457 from AbrarSyed/master

implemented crowdin support
Add username cache for determining a player's last known username
Merge pull request #1368 from matthewprenger/patch-1

Added username cache
Fix for biome weights under 10

This solves the problem where custom mod biomes with weights under 10
not being generated in the world.

Cleaned up the code and made the patch smaller
Merge pull request #1461 from Azanor/master

 Fix for biome weights under 10
Fix logic error in Blodd's Snapshot capture that caused blocks to not be updated to the client. Closes #1451