LOS ANGELES — As the fifth-season adventures of “Grace and Frankie ” begin, viewers can rest assured there’s more to come. Series creator Marta Kauffman and Netflix said Tuesday that the series starring Jane Fonda and Lily Tomlin has been renewed for season six, due in 2020. Kauffman said she was hopeful the comedy would keep going, given that “we certainly feel the love” from streaming service Netflix. But the decision announced before today’s season-five release “is greatly appreciated,” she said.