Update Documentation:Repository:Meta-Packages.php

updated for 14.04
    1. updated repo enabling and install
    2. xfce no longer supported or at least command line didn't work. Removed It.
    3. on step 4 fixed typo ( I believe) changed if to is
    4. removed kxstudio-meta-nonfree from meta-packages
    5. changed kernel to linux-lowlatency none of the other seem to be working.
    5. step 6 clarified for 14.04 after kxstudio welcome screen logs into unity must logout of
    unity and log into kde plasma to get kxstudio default DE and theme.

12.04 went through same instructions with 12.04 not sure if you will be supporting 12.04 or not. Some issues with a few things. So instruction's won't work. If you want I can make a bug report on launchpad. Not sure if issues are minor or not.