Explain which groups can have branch access

app/views/projects/protected_branches/_create_protected_branch.html.haml

@@ -36,6 +36,10 @@
                              options: { toggle_class: 'js-allowed-to-push js-multiselect wide',
                              dropdown_class: 'dropdown-menu-user dropdown-menu-selectable', filter: true,
                              data: { input_id: 'push_access_levels_attributes', default_label: 'Select' } })
+            .help-block
+              Only groups that
+              = link_to 'have this project shared', help_page_path('workflow/share_projects_with_other_groups')
+              can be added here
 
     .panel-footer
       = f.submit 'Protect', class: 'btn-create btn', disabled: true