Fix link in contributing guidelines

Author: awvwgk

CONTRIBUTING.rst

@@ -74,7 +74,7 @@ For New Contributors
 ~~~~~~~~~~~~~~~~~~~~
 
 If you never created a pull request before, welcome :tada:.
-You can learn how from `this great tutorial <https://egghead.io/series/how-to-contribute-to-an-open-source-project-on-github>`_.
+You can learn how from `this great tutorial <https://app.egghead.io/courses/how-to-contribute-to-an-open-source-project-on-github>`_.
 
 Don't know where to start?
 You can start by looking through these `help-wanted issues <https://github.com/grimme-lab/xtb/issues?q=label%3A%22help+wanted%22+is%3Aissue+is%3Aopen>`_.