Reviewed by Darin Adler.

        Update contributing.html to mention recently added tools.
        https://bugs.webkit.org/show_bug.cgi?id=29318

        Update our contributing instructions to mention
        the new tools (check-webkit-style and commit-queue)
        recently added to make contributions easier.

        * coding/contributing.html:
         - Mention check-webkit-style as an optional helper tool.
         - Mention checking the 'patch' checkbox.
         - Mention the commit-queue as an optional helper tool.
         - Remove "or in email" since patch reviews are all done via bugzilla.
         - Encourage contributers to be responsible for getting their patch landed.  Provide a list of committers.
         - Mention commit-queue as an optional help in getting your patch landed.
         - Give an overview of the commit-queue process and link to the Commit Queue docs.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@48488 268f45cc-cd09-0410-ab3c-d52691b4dbfc