Ganga page needs updating

[mesmith75]

The page on submitting cmake tasks with Ganga needs updating now it is properly supported with GaudiExec.

[mesmith75]

Also on the same page it needs updating to git lb-checkout

[alexpearce]

Thanks for pointing this out, you're quite right. Would you be willing to write a lesson on it? I think it would be very helpful to have something.

[mesmith75]

Sure, I'll edit the current one - and update the svn reference to gitlab.