Compares headings from 2 documents
E.g.
python3 headingdiff.py https://docs.redhat.com/en/documentation/red_hat_developer_hub/1.2/html-single/getting_started_with_red_hat_developer_hub/index https://docs.redhat.com/en/documentation/red_hat_developer_hub/1.1/html-single/getting_started_with_red_hat_developer_hub/index
Ensure the URLs are the single page version of the docs pages.