Add info about failing pre-commit hook (#3362)

* add info about failing pre-commit hook

* review

---------

Co-authored-by: Falko Schindler <falko@zauberzeug.com>

CONTRIBUTING.md

@@ -90,6 +90,11 @@ pre-commit run --all-files
 ```
 
 These checks will also run automatically before every commit.
+The command may fail with
+
+> RuntimeError: failed to find interpreter for Builtin discover of python_spec='python3.8'
+
+You will need to install Python 3.8 and make sure it is available in your `PATH`.
 
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