ContributingCode wiki updates

[Colin Barrett]

Hi all,

I've updated the ContributingCode page to include a bunch of Mercurial  
specific information. Please feel free to take a look over and either  
update the page with more information or send feedback to me.

I decided to do this update after getting two or three emails about  
patches the past couple weeks about patches and I began to wonder why  
we were still instructing people to use .diff files in this glorious  
new age of DVCS ;)

http://trac.adium.im/wiki/ContributingCode

Cheers,
-Colin