Add contributing guide

This is essentially a straight copy from the documentation, but
I updated the list of available languages.

CONTRIBUTING.md

@@ -0,0 +1,100 @@
+# Contribute
+
+Want to show Sinatra some love? Help out by contributing!
+
+## Find a bug?
+
+Log it in our [issue tracker][ghi] or send a
+note to the [mailing list][ml].
+Be sure to include all relevant information, like the versions of Sinatra and
+Ruby you're using. A [gist](http://gist.github.com/) of the code that caused
+the issue as well as any error messages are also very helpful.
+
+## Need help?
+
+The [Sinatra mailing list][ml] has over 900 subscribers, many of which are happy
+to help out newbies or talk about potential feature additions. You can also drop by
+the [#sinatra](irc://chat.freenode.net/#sinatra) channel on
+[irc.freenode.net](http://freenode.net).
+
+## Have a patch?
+
+Bugs and feature requests that include patches are much more likely to
+get attention. Here are some guidelines that will help ensure your patch
+can be applied as quickly as possible:
+
+1. **Use [Git](http://git-scm.com) and [GitHub](http://github.com):**
+   The easiest way to get setup is to fork the
+   [sinatra/sinatra repo](http://github.com/sinatra/sinatra/).
+   Or, the [sinatra.github.com repo](http://github.com/sinatra/sinatra.github.com/),
+   if the patch is doc related.
+
+2. **Write unit tests:** If you add or modify functionality, it must
+   include unit tests. If you don't write tests, we have to, and this
+   can hold up acceptance of the patch.
+
+3. **Mind the `README`:** If the patch adds or modifies a major feature,
+   modify the `README.md` file to reflect that. Again, if you don't
+   update the `README`, we have to, and this holds up acceptance.
+
+4. **Update the Changelog (`CHANGES`):** The changelog helps give an
+   overview of the changes that go into each release, and gives credit
+   where credit is due. We make sure that the Changelog is up to date
+   before each release, and we always appreciate it when people make
+   it easier to get the release out the door.
+
+5. **Push it:** Once you're ready, push your changes to a topic branch
+   and add a note to the ticket with the URL to your branch. Or, say
+   something like, "you can find the patch on johndoe/foobranch". We also
+   gladly accept GitHub [pull requests](http://help.github.com/pull-requests/).
+
+__NOTE:__ _we will take whatever we can get._ If you prefer to
+attach diffs in emails to the mailing list, that's fine; but do know
+that _someone_ will need to take the diff through the process described
+above and this can hold things up considerably.
+
+## Want to write docs?
+
+The process for contributing to Sinatra's website, documentation or the book
+is the same as contributing code. We use git for versions control and
+GitHub to track patch requests.
+
+* [The sinatra.github.com repo](http://github.com/sinatra/sinatra.github.com/)
+  is where the website sources are managed. There are almost always people in
+  `#sinatra` that are happy to discuss, apply, and publish website patches.
+
+* [The Book](http://sinatra-book.gittr.com/) has its own [git
+  repository](http://github.com/sinatra/sinatra-book/) and build process but is
+  managed the same as the website and project codebase.
+
+* [Sinatra Recipes](http://recipes.sinatrarb.com/) is a community
+  project where anyone is free to contribute ideas, recipes and tutorials. Which
+  also has its own [git
+  repository](http://github.com/sinatra/sinatra-recipes).
+
+* [The Introduction](http://www.sinatrarb.com/intro.html) is generated from
+  Sinatra's [README file](http://github.com/sinatra/sinatra/blob/master/README.md).
+
+* If you want to help translating the documentation, the README is already available in
+  [Japanese](http://github.com/sinatra/sinatra/blob/master/README.ja.md),
+  [German](http://github.com/sinatra/sinatra/blob/master/README.de.md),
+  [Chinese](https://github.com/sinatra/sinatra/blob/master/README.zh.md),
+  [Russian](https://github.com/sinatra/sinatra/blob/master/README.ru.md),
+  [European](https://github.com/sinatra/sinatra/blob/master/README.pt-pt.md) and
+  [Brazillian](https://github.com/sinatra/sinatra/blob/master/README.pt-br.md) Portugese,
+  [French](https://github.com/sinatra/sinatra/blob/master/README.fr.md),
+  [Spanish](https://github.com/sinatra/sinatra/blob/master/README.es.md),
+  [Korean](https://github.com/sinatra/sinatra/blob/master/README.ko.md), and
+  [Hungarian](https://github.com/sinatra/sinatra/blob/master/README.hu.md).
+  The translations tend to fall behind the English version. Translations into other
+  languages would also be appreciated.
+
+## Looking for something to do?
+
+If you'd like to help out but aren't sure how, pick something that looks
+interesting from the [issues][ghi] list and hack on. Make sure to leave a
+comment on the ticket noting that you're investigating (a simple "Taking..."
+is fine).
+
+[ghi]: http://github.com/sinatra/sinatra/issues
+[ml]: http://groups.google.com/group/sinatrarb/topics "Sinatra Mailing List"