Add link to "feature branch workflow"

[ciskip]

CONTRIBUTING.md

@@ -1,7 +1,7 @@
 ## Understanding the basics
 We welcome contributions to JabRef and encourage to create a fork, clone, **create a new branch** (such as `fix-for-issue-121`), **work on the new branch — not master**, and create a pull request.
 Be sure to create a **separate branch** for each improvement you implement.
-Take a look at GitHub's excellent [help documentation] for a detailed explanation.
+Take a look at GitHub's excellent [help documentation] for a detailed explanation and the explanation of [Feature Branch Workflow](https://de.atlassian.com/git/tutorials/comparing-workflows#feature-branch-workflow) for the idea behind this kind of development.
 
 We also have [code howtos](https://github.com/JabRef/jabref/wiki/Code-Howtos) and [guidelines for setting up a local workspace](https://github.com/JabRef/jabref/wiki/Guidelines-for-setting-up-a-local-workspace).