Add release instructions

CONTRIBUTING.md

@@ -24,6 +24,43 @@ bundle
 [Run the test suite](#testing) to check everything works as expected.
 
 
+## Releasing
+
+The following instructions uses `$VERSION` as a placeholder, where `$VERSION` is a `MAJOR.MINOR.BUGFIX` release such as `1.2.0`.
+
+1. Set the version in `version.rb`:
+
+    ```ruby
+    VERSION = "$VERSION"
+    ```
+
+1. Run the test suite and ensure all the tests pass.
+
+1. Finalize the `## master` section in `CHANGELOG.md` assigning the version.
+
+1. Commit and push the changes
+
+    ```shell
+    git commit -a -m "Release $VERSION"
+    git push origin master
+    ```
+
+1. Wait for CI to complete.
+
+1. Create a signed tag.
+
+    ```shell
+    git tag -a v$VERSION -s -m "Release $VERSION"
+    git push origin --tags
+    ```
+
+1. Release to RubyGems.
+
+    ```shell
+    gem push pkg/<filename>
+    ```
+
+
 ## Testing
 
 To run the test suite: