Add update instructions

README.md

@@ -14,10 +14,14 @@ Alternatively, you can add the following to your project's Gemfile:
 
 *Note: You are not required to install Jekyll separately. Once the `github-pages` gem is installed, you can build your site using `jekyll build`, or preview your site using `jekyll serve`.*
 
+## Updating
+
+To update to the latest version of Jekyll and associated dependencies, simply run `gem update github-pages`, or if you've installed via Bundler, `bundle update github-pages`.
+
 ## Building
 
 To build a new version of the gem, run `script/build`
 
 ## License
 
-Distributed under the [MIT License](LICENSE).
+Distributed under the [MIT License](LICENSE).