sub_project_guidelines: Document the procedure to make a branch EOL
sub_project_guidelines: Document the procedure to make a branch EOL

Change-Id: Ifa1a466e6ede6b2fa9335eca523b66f3fd7af571

sebrandon1/neutron,huntxu/neutron,mahak/neutron,cloudbase/neutron,dims/neutron,cloudbase/neutron,wolverineav/neutron,dims/neutron,eayunstack/neutron,openstack/neutron,sebrandon1/neutron,mahak/neutron,noironetworks/neutron,eayunstack/neutron,noironetworks/neutron,MaximNevrov/neutron,bigswitch/neutron,igor-toga/local-snat,MaximNevrov/neutron,openstack/neutron,huntxu/neutron,wolverineav/neutron,igor-toga/local-snat,klmitch/neutron,klmitch/neutron,openstack/neutron,mahak/neutron,bigswitch/neutron