Practice Fusion, provider of a free electronic health record service for doctors, bought app developer Ringadoc on Wednesday as it moves into a new market: telemedicine. Ringadoc, a startup previously based in Practice Fusion’s San Francisco offices, has developed a mobile application and web service for doctors to manage after-hours patient calls. It was an attractive target for Practice Fusion, Chief Executive Ryan Howard said, as “it’s a base product that every doctor needs.” “This is us diversifying our portfolio,” Howard said, adding that Practice Fusion is planning to launch a host of services complementary to its best-known product, its health records. Silicon Valley has made a big bet on Practice Fusion in recent years.