docs: explain why specifying 'cms' service

lms/djangoapps/course_home_api/course_metadata/views.py

@@ -140,6 +140,11 @@ def get(self, request, *args, **kwargs):
             'can_view_certificate': certificates_viewable_for_course(course),
             'course_modes': course_modes,
             'is_new_discussion_sidebar_view_enabled': new_discussion_sidebar_view_is_enabled(course_key),
+            # We check the course author access in the context of CMS here because this field is used
+            # to determine whether the user can access the course authoring tools in the CMS.
+            # This is a temporary solution until the course author role is split into "Course Author" and
+            # "Course Editor" as described in the permission matrix here:
+            # https://github.com/openedx/platform-roadmap/issues/246
             'has_course_author_access': has_course_author_access(request.user, course_key, 'cms'),
         }
         context = self.get_serializer_context()