Add a .gitattributes file to prevent git from treating FITS files as text files

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2182 ed100bfc-0583-0410-97f2-c26b58777a21
Emphasize that the .authors file should be configured before synchronizing with SVN--forgetting to do this was causing me some pretty nasty problems

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2185 ed100bfc-0583-0410-97f2-c26b58777a21