Add GitHub Flow Guide link

Author: jordanmccullough

foundations/index.md

@@ -304,7 +304,7 @@ A branch is a divergent path in the history of the code base. It may contain an
 
 {% capture lab %}
 1. Create a Fork of a repository needing contributions
-2. Follow the contribution pattern of the GitHub Flow, with the branch creation and commits happening on your fork of the repository
+2. Follow the contribution pattern of the [GitHub Flow](https://guides.github.com/introduction/flow/), with the branch creation and commits happening on your fork of the repository
 3. Observe the Network and Members graph that offer visualizations of your commits and fork
 4. Merge the pull request
 5. Observe your contributions in the original repository, having preserved your username as the author of the code