PM representative responsibilities added
PM representative responsibilities added

With regards to the PM meeting [conversation](https://docs.google.com/document/d/1ZElyRqNsGebvMpikEBhSuf2Q6WrEYHB2PgWIlGgwt78/edit?ts=58740b3d#heading=h.1txgejyk87dr), SIG representative functions for the PM group are described.
kubernetes/community,bgrant0607/community,pwittrock/community,kubernetes/community,bgrant0607/community,kubernetes/community,pwittrock/community