Here’s how you know blogging has reached the mainstream: chefs — notoriously short on time, and mostly workaholics — have somehow made time for the pursuit. Some blogs, such as the one kept by cook Richie Nakano of Nopa (linecook415.blogspot.com) offer a behind-the-scenes look at a busy SF restaurant. Others, such as the one written by Brett Emerson, owner and chef at the forthcoming Noe Valley restaurant Contigo (inpraiseofsardines.typepad.com), chronicle the harrowing process of opening a restaurant in the city.