Add example commits for our formatting best practice

Author: mfisher87

doc/contributing.md

@@ -34,4 +34,6 @@ trigger this manually with `pre-commit run --all-files`.
 Thanks to pre-commit, all commits should be formatted. In cases where formatting needs
 to be fixed (e.g. changing config of a linter), a format-only commit should be created,
 and then another commit should immediately follow which updates
-`.git-blame-ignore-revs`.
+`.git-blame-ignore-revs`. For example:
+[1fec42d](https://github.com/matplotlib/viscm/pull/64/commits/1fec42d0baf90e00d510efd76cb6006fa0c70dc4),
+[8aa7bb0](https://github.com/matplotlib/viscm/pull/64/commits/8aa7bb01440aeca6f8bbcefe0671c28f2ce284c6).