Update CONTRIBUTING.md

CONTRIBUTING.md

@@ -5,6 +5,6 @@ Be nice:
     * work in a branch of your fork
     * make a pull request to merge your branch to the master
  
-Don't know how to do this? [Read our guide](gitBranches.md).
+Don't know how to do this? [Read our guide](howTo/gitBranches.md).
  
 Need more info? Read the excellent [contributing to opensource code](https://opensource.guide/how-to-contribute/) guidance.
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