doc: clarify commit email requirements in contribution guidelines

Updated the contribution guidelines to specify that pseudo or anonymized
emails (e.g., GitHub noreply addresses) are not allowed for commits.

Signed-off-by: Maxwell Weru <[email protected]>

Author: mburumaxwell

doc/contribute/guidelines.rst

@@ -176,8 +176,11 @@ For your commits, replace:
 - ``Your Name`` with your legal name (pseudonyms, hacker handles, and the
   names of groups are not allowed)
 
-- ``[email protected]`` with the same email address you are using to
-  author the commit (CI will fail if there is no match)
+- ``[email protected]`` with the real email address you are using to
+  author the commit. Pseudo or anonymized emails such as
+  ``[email protected]`` are not allowed. The
+  email must match the one you use to author the commit (CI will fail if
+  there is no match).
 
 You can automatically add the Signed-off-by: line to your commit body using
 ``git commit -s``. Use other commits in the zephyr git history as examples.