This improves method detection for Ruby source files;
making output of "git diff" and "git log -p -W" more
readable for git users looking at our Ruby code.

git will automatically notice this file and start using
it when generating diff output.

See the gitattributes(5) manpage for more details.
Ruby pattern definitions reside in userdiff.c of the
git sources at git://git.kernel.org/pub/scm/git/git.git

* .gitattributes: new file for git users
  [ruby-core:71578] [Feature #11713]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52674 b2dd03c8-39d4-4d8f-98ff-823fe69b080e