Few people would say that saving for retirement is easy. But the process is especially difficult for people who work part time or who freelance for a simple reason: they are much less likely to have access to a retirement account through their jobs. Now Uber is trying to change that for its drivers by partnering with the robo-adviser Betterment to give drivers access to individual retirement accounts. Starting Wednesday, tens of thousands of drivers in Seattle, Boston, Chicago and New Jersey should be able to sign up for an IRA or a Roth IRA using their Uber apps.