Add documentation for the external_url option
Add documentation for the external_url option

gitlabhq/omnibus-gitlab,aleksandrs-ledovskis/omnibus-gitlab,felixbuenemann/omnibus-gitlab,aleksandrs-ledovskis/omnibus-gitlab,felixbuenemann/omnibus-gitlab,gitlabhq/omnibus-gitlab,copystudy/omnibus-gitlab,felixbuenemann/omnibus-gitlab,copystudy/omnibus-gitlab,aleksandrs-ledovskis/omnibus-gitlab,copystudy/omnibus-gitlab,gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab