Boston Public Schools officials are opening up so-called “pop-up centers” across the city in hopes of helping families arriving from storm-ravaged Puerto Rico sign up for school, find housing, and get necessities such as food and clothing.Beginning tomorrow, BPS will team up with community organizations Inquilinos Boricuas en Accion, South Boston en Accion, and Sociedad Latina to link arriving families with services, both at the organizations’ headquarters and several district welcome centers, Superintendent Tommy Chang announced in a letter Friday.