simplifies installation instructions in README
simplifies installation instructions in README

sdss/marvin,sdss/marvin,albireox/marvin,bretthandrews/marvin,bretthandrews/marvin,albireox/marvin,sdss/marvin,albireox/marvin,bretthandrews/marvin,sdss/marvin,bretthandrews/marvin,albireox/marvin