BostonGlobe.com, which launched last month and was initially available to readers on a free trial basis, is charging for access to its content today, Globe officials said. The Globe is offering a special promotional subscription to the new site - 99 cents for the first four weeks. After that, subscription to BostonGlobe.com will cost $3.99 a week. Subscribers to the Globe’s print edition will not have to pay extra for access to BostonGlobe.com.