Add a note about not modifying the git history to the quick guide (GH-588)

Co-authored-by: Kyle Stanley <[email protected]>
Co-authored-by: Terry Jan Reedy <[email protected]>
Co-authored-by: Carol Willing <[email protected]>

Author: 4 people

pullrequest.rst

@@ -47,6 +47,11 @@ Here is a quick overview of how you can contribute to CPython:
 .. [*] If an issue is trivial (e.g. typo fixes), or if an issue already exists,
        you can skip this step.
 
+.. note::
+   In order to keep the commit history intact, please avoid squashing or amending
+   history and then force-pushing to the PR. Reviewers often want to look at
+   individual commits.
+
 .. _Clear communication: https://opensource.guide/how-to-contribute/#how-to-submit-a-contribution
 .. _Open Source: https://opensource.guide/
 .. _create an issue: https://bugs.python.org/