test days live image creation guide

[Kamil Paral]

Our test day kickstart script was oficially accepted [1] by the 
Spins SIG and is available in the spin-kickstarts project [2]
(thanks to Bruno Wolff III).

I have modified the guide accordingly - thanks to having it upstream
it is now much simpler than before [3].

[1] https://fedoraproject.org/wiki/QA_Test_Day_Spin
[2] http://git.fedorahosted.org/git/spin-kickstarts.git
[3] https://fedoraproject.org/wiki/QA/Test_Days/Live_Image