On weekends, LaNeisha, a 33-year-old in San Francisco, borrows a friend’s car to drive for Uber. When she discovered that she could rent out her closet for $290 through a startup called Roost, she turned it into a storage unit. She finds other gigs on Craiglist. For LaNeisha, who struggled to find work otherwise, it’s a way to survive. But it’s not easy. A new report looks at the workers of the on-demand economy—from Lyft…