Improve documentation on core/memory specification
Improve documentation on core/memory specification

vladsaveliev/bcbio-nextgen,brainstorm/bcbio-nextgen,chapmanb/bcbio-nextgen,a113n/bcbio-nextgen,biocyberman/bcbio-nextgen,lbeltrame/bcbio-nextgen,brainstorm/bcbio-nextgen,brainstorm/bcbio-nextgen,biocyberman/bcbio-nextgen,chapmanb/bcbio-nextgen,lbeltrame/bcbio-nextgen,a113n/bcbio-nextgen,biocyberman/bcbio-nextgen,a113n/bcbio-nextgen,lbeltrame/bcbio-nextgen,vladsaveliev/bcbio-nextgen,vladsaveliev/bcbio-nextgen,chapmanb/bcbio-nextgen