README: Added documentation about targets
README: Added documentation about targets

oli-obk/atom-build,noseglid/atom-build,gregerolsson/atom-build,gogoprog/atom-build,sphaerophoria/atom-build,forivall/atom-build,MackieLoeffel/atom-build,bwinton/atom-build,5n8ke/atom-build,MadcapJake/atom-build,jhasse/atom-build