DOCUMENTATION

[maxulysse]

Add proper documentation to explain how to properly use it and implement it in the pipelines

[maxulysse]

I feel like rnaseq currently use the igenomes.config file properly (but does not use igenomes anymore).
And sarek use the igenomes.config file properly, and fully uses igenomes.
I'm a bit unsure about the rest of the other pipelines, so we'll need to explain that properly.
(thinking keys/map/params, and so on)