add documentation for current release process

RELEASING.md

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+# Release standards
+
+Here's where we document how homebrew-cask is released.
+
+## Versioning
+
+We attempt to follow [Semantic Versioning](http://semver.org/) as much as
+possible.
+
+Since we are still pre-1.0, this essentially means that we bump the PATCH
+number when we fix bugs, and we bump the MINOR number when we add stuff. Pretty
+simple.
+
+## Release Process
+
+We'll get this scripted someday, but until then it's better to have it written
+down then floating in a brain somewhere.
+
+1. Bump the version, which is stored in the `brew-cask.rb` formula. We
+   simultaneously bump the `url` as well as the `version` line.
+2. Make a commit with just the version bump. Something like `git commit -m
+  'bump version to v0.13.0'`.
+3. Tag that commit, ensuring that you provide a message so we get an annotated
+   tag. Like this: `git tag -m v0.13.0 v0.13.0`
+4. Push the commit and the tag: `git push --follow-tags`
+5. Rejoice!
+
+## Things to consider
+
+The way `brew update` works, users will always be tracking `HEAD` in their tap.
+This means that the latest updates to Casks are going to trickle out
+immediately after push. This means there are times when we need to be
+thoughtful about how we push out new or breaking functionality. As a pre-1.0
+project we can still break backwards compatibility, but sometimes there might
+be decisions we can make about releasing to make things easier on our users.
+
+In general: go easy on the users!