Create ---feature.md (#6129)
Create ---feature.md (#6129)

This will be used as a template when adding a new feature request.
Note that it will auto-add the `Feature 🎁` label.
mkaply/firefox-ios,AaronMT/firefox-ios,st3fan/firefox-ios,AaronMT/firefox-ios,st3fan/firefox-ios,StYaphet/firefox-ios,Acidburn0zzz/firefox-ios,st3fan/firefox-ios,flodolo/firefox-ios,mkaply/firefox-ios,garvankeeley/firefox-ios,AaronMT/firefox-ios,Acidburn0zzz/firefox-ios,garvankeeley/firefox-ios,Acidburn0zzz/firefox-ios,Acidburn0zzz/firefox-ios,flodolo/firefox-ios,StYaphet/firefox-ios,StYaphet/firefox-ios,AaronMT/firefox-ios,AaronMT/firefox-ios,st3fan/firefox-ios,st3fan/firefox-ios,Acidburn0zzz/firefox-ios,garvankeeley/firefox-ios,flodolo/firefox-ios,mozilla-mobile/firefox-ios,garvankeeley/firefox-ios,StYaphet/firefox-ios,mozilla-mobile/firefox-ios,mozilla-mobile/firefox-ios,st3fan/firefox-ios,StYaphet/firefox-ios,AaronMT/firefox-ios,flodolo/firefox-ios,mozilla-mobile/firefox-ios,flodolo/firefox-ios,StYaphet/firefox-ios,garvankeeley/firefox-ios,st3fan/firefox-ios,mkaply/firefox-ios,mozilla-mobile/firefox-ios,mkaply/firefox-ios,mkaply/firefox-ios,Acidburn0zzz/firefox-ios,garvankeeley/firefox-ios,mozilla-mobile/firefox-ios,garvankeeley/firefox-ios,mkaply/firefox-ios,flodolo/firefox-ios,mozilla-mobile/firefox-ios,mkaply/firefox-ios,st3fan/firefox-ios,flodolo/firefox-ios,StYaphet/firefox-ios,AaronMT/firefox-ios,Acidburn0zzz/firefox-ios,StYaphet/firefox-ios,Acidburn0zzz/firefox-ios