I started gathering links for you, but it's easier just to provide the source of all the links: <a href="https://www.google.com/search?rls=en&q=github+postmortem&ie=UTF-8&oe=UTF-8" rel="nofollow">https://www.google.com/search?rls=en&q=github+postmortem&ie=...</a>
Check out this talk: <a href="https://help.statuspage.io/knowledge_base/topics/postmortems" rel="nofollow">https://help.statuspage.io/knowledge_base/topics/postmortems</a>