Build Instructions for KWin

On poular request I added a section on How to Build KWin to our Wiki. This aims to those who want to work on KWin but do not want to build all the dependencies and the other parts of the Plasma Workspaces.

I hope this can help some people to test and develop on KWin. In case you find any errors in the instructions, please let me know. I tested the instructions yesterday on my Pandaboard and it compiled KWin master against a dev environment of Ubuntu 12.04, so they seem to be correct 😉