Melissa Etheridge has been added to the bill at Tanglewood. The smoky-voiced singer will perform at the Boston Symphony Orchestra’s summer home June 21, BSO officials announced Wednesday. The next night, Tanglewood will present the Jerry Garcia Symphonic Celebration, a new project celebrating the songs of the late Grateful Dead leader featuring Warren Haynes with conductor Keith Lockhart and the Boston Pops. The orchestral adventure will feature new arrangements of some of Garcia’s classic songs. Previously announced shows at the shed in Lenox include Jackson Browne on July 4, and Grammy winner Esperanza Spalding on Aug. 4.