A week after organic produce powerhouse Whole Foods Market opened on Gilman Street, a Georgia purveyor of gourmet burgers added to the cosmopolitan melange of this rapidly gentrifying West Berkeley commercial strip. Farm Burgers opened right across Gilman on Ninth Street last week in a converted light industrial building that it shares with two other recent arrivals: Philz Coffee , in July, and Doughnut Dolly, in August.