Add documentation about releasing the gem

Why:

* It should be fairly easy to find documentation on releasing the gem.

Author: Greg Lazarev

RELEASING.md

@@ -0,0 +1,10 @@
+# Releasing
+
+1. Ask to be added as an owner for this gem on RubyGems.org.
+1. Update the `VERSION` constant.
+1. Run `bundle update` to update `Gemfile.lock`.
+1. Run the test suite.
+1. Edit `NEWS`, `Changelog`, or `README` files if relevant.
+1. Commit changes. Use the convention "v2.1.0" in your commit message.
+1. Run `rake release`, which tags the release, pushes the tag to GitHub, and
+   pushes the gem to RubyGems.org.