added netrc information in the installation page
added netrc information in the installation page

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