Mayor Thomas M. Menino is launching a blog to help the city transition to a new administration, his spokeswoman said. The blog will formally launch on Saturday, with 100 days left in Menino’s term, said spokeswoman Dot Joyce. It will be updated daily with information about city departments and neighborhoods, according to Joyce. She said in a prepared statement that the “goal of the blog is to provide insight on policies and procedures” along with video packages and other items. It will be available at next.cityofboston.gov.