* ext/io/nonblock/nonblock.c: [DOC] Document io/nonblock by reprah
  [Fixes GH-418] https://github.com/ruby/ruby/pull/418 based on the
  original discussion from documenting-ruby/ruby#18


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43314 b2dd03c8-39d4-4d8f-98ff-823fe69b080e