The Editing the guidelines page describes how to create a pull request, to request changes to the document. This includes the instruction to click on the "Edit on GitHub" link:
- Click “Edit on GitHub” in the top right corner
Unfortunately, there currently is no "Edit on GitHub" link on the pages I checked.
The place where that link would be shown, now provides a "View page source" link. This link provides the raw (text, markdown-like syntax) version of the page, seemingly hosted outside of github. This provides no direct way to edit the corresponding page.
Either the Contributing page should be updated with new information or the "Edit on GitHub" link should be reinstated.