[coreboot] wiki update patch command

Hello,
I hope no one minds, I just updated the
http://www.coreboot.org/Development_Guidelines
page and added a little comment on how to use "patch" to test patches  
against your clean local repository. Here is what it says:

Testing your Patch

Patches can be tested against your clean local repository by using the  
patch command. Just copy your new patch file to the top-level  
directory of your clean local repository and issue this command:

patch -p0 < filename.patch

Thanks - Joe