Add short documentation about PRE_GENERATE_APKS in settings changelog (bug 978165)
Add short documentation about PRE_GENERATE_APKS in settings changelog (bug 978165)

ddurst/zamboni,luckylavish/zamboni,elysium001/zamboni,jasonthomas/zamboni,ddurst/zamboni,kumar303/zamboni,ddurst/zamboni,mozilla/zamboni,mozilla/zamboni,jasonthomas/zamboni,mudithkr/zamboni,Hitechverma/zamboni,jamesthechamp/zamboni,andymckay/zamboni,Hitechverma/zamboni,ayushagrawal288/zamboni,eviljeff/zamboni,jamesthechamp/zamboni,ayushagrawal288/zamboni,shahbaz17/zamboni,tsl143/zamboni,jamesthechamp/zamboni,Jobava/zamboni,ingenioustechie/zamboni,tsl143/zamboni,shahbaz17/zamboni,ddurst/zamboni,kumar303/zamboni,Hitechverma/zamboni,diox/zamboni,ngokevin/zamboni,jasonthomas/zamboni,Jobava/zamboni,ayushagrawal288/zamboni,mstriemer/zamboni,ngokevin/zamboni,washort/zamboni,washort/zamboni,jamesthechamp/zamboni,ingenioustechie/zamboni,andymckay/zamboni,Jobava/zamboni,eviljeff/zamboni,ayushagrawal288/zamboni,mudithkr/zamboni,ngokevin/zamboni,Jobava/zamboni,elysium001/zamboni,elysium001/zamboni,kumar303/zamboni,mozilla/zamboni,mudithkr/zamboni,andymckay/zamboni,mstriemer/zamboni,clouserw/zamboni,diox/zamboni,eviljeff/zamboni,mstriemer/zamboni,mstriemer/zamboni,tsl143/zamboni,jasonthomas/zamboni,eviljeff/zamboni,luckylavish/zamboni,washort/zamboni,clouserw/zamboni,kumar303/zamboni,luckylavish/zamboni,clouserw/zamboni,washort/zamboni,tsl143/zamboni,elysium001/zamboni,ingenioustechie/zamboni,luckylavish/zamboni,clouserw/zamboni,shahbaz17/zamboni,diox/zamboni,ingenioustechie/zamboni,mudithkr/zamboni,shahbaz17/zamboni,Hitechverma/zamboni,diox/zamboni,mozilla/zamboni