The current ext-docs branch is about two milestones behind master and there have been several extensibility topic updates in master which need to be manually ported since the relevant content has moved to a new location.

A couple of examples are:
The PAT token recommendations #2230
Removing Travis and AppVeyor from testing-extensions 7125bcf

We'll need to walk the history for /docs/extensions and /docs/extensionAPI to find changes and manually bring them into ext-docs.