Hi @jbielecki,
The "Discussion Summary" feature you're referencing is in what's called a "feature preview" state right now, meaning Instructure is still working on the feature but let's school/institution admins enable if they choose. Things that are in a feature preview state are more likely to change often, and usually aren't enabled by a majority of institutions (at least not right away). Because of these reasons, and probably others too, Instructure doesn't tend to have official guides for previews. There are sometimes special user groups or announcements in the community about the preview though (which I think you found for this in another thread). As a Canvas admin myself, when our institution chooses to enable a feature preview, we definitely communicate it to our faculty, and we also make it an opt-in experience whenever that's possible. The philosophy works well for us, but each school/institution really chooses their own path around this. Maybe a message will be coming to you soon announcing the availability.
While there are sometimes bumps in the road, I would personally say that Instructure does a better job than most other vendors at 1 - having a plethora of documentation available to the general public and 2 - keeping the info up to date. We definitely find a outdated document here and there or some change that didn't seem to be documented anywhere, and we definitely speak up in those cases. I always try to keep the big picture in mind though, and that's why I would generally rate Instructure pretty highly overall in this area.
Just my two cents worth on the topic...
-Chris