docs: explain how to find a clang-format patch generated by CI (#4521)

CONTRIBUTING.md

@@ -119,6 +119,16 @@ this:
 You can format individual files in place by running `clang-format -i <file>...`
 from any directory within this project.
 
+There is a Continuous Integration job that runs clang-format on pull requests. If the code doesn't comply, a patch file that corrects auto-fixable formatting issues is generated.
+
+To download the patch file:
+
+1. Next to `clang-format / check (pull_request) Failing after #s` -> click **Details** to open the details page.
+2. Left menu -> click **Summary**
+3. Scroll down to near the bottom-right under `Artifacts` -> click **clang-format.patch**
+4. Download the zip file and extract it to your local git repository. Run `git apply [patch-file-name]`.
+5. Commit and push.
+
 You can install a pre-commit hook to automatically run `clang-format` before every commit:
 ```
 pip3 install pre-commit