Add documentation on quick actions for add/remove epic parent relations.
Add documentation on quick actions for add/remove epic parent relations.

mmkassem/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,stoplightio/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq,mmkassem/gitlabhq