Update docs/contributing/core/index.md

Co-authored-by: Maurits van Rees <[email protected]>

Author: stevepiercy

docs/contributing/core/index.md

@@ -105,6 +105,7 @@ Notice that the script expects Python 3.11 to be installed on your system and in
 ```
 
 Edit it according to the Python version you want to use, then save and close the file.
+After you have run the script you should undo the change, otherwise you have a local change in git that you might accidentally commit.
 ````
 
 Now run the script to install Plone 6.