Documenting a lousy interface is not a solution— it's a mitigation strategy and usually a lazy one. Most people find git's interface to be confusing, arbitrary, and frequently astonishing in destructive ways. Maybe you're exceptionally gifted in keeping a large bank of seemingly arbitrary commands in your head, or maybe you speak git frequently enough to have native proficiency. Unfortunately, you can't generalize that to all other users, and it doesn't invalidate their difficulty.
Since most folks new to git are likely new to CLIs— having a tutorial two levels deep in man pages makes it nearly useless. If you draw two barely touching circles on a page and label one "people confused by git enough to need a tutorial," and the other "people who know what man pages are, how to access and read them, and think to look there for tutorials,"— that's your usability Venn diagram for that documentation. Beyond that, many organizations require non-developers to use git now— copywriters, designers, project managers, etc. We're not talking about sendmail or clang here.
That lack of developer empathy for less technical end-users is why software projects, especially FOSS ones, marginalize UX input. Usability is the one thing commercially-sold software consistently does better than FOSS, and one of the reasons commercial offerings so frequently trounce FOSS equivalents in everything but developer and system/network tools used by people with bad UI Stockholm Syndrome. When monetary incentives and non-developer input inform product decisions, "it's in the docs" just doesn't cut it.
I've primarily worked in tech for the past 25 years, been a full-time developer for 10 (exclusively writing FOSS,) and have recently moved towards design because I see a lot of unmet needs there. So I understand the frustration in user needs precluding the most elegant/interesting/efficient technical solution to a problem. But, if you aren't actively working to meet end-user needs, frustration about end-user confusion isn't particularly justified.
As an aside, I believe Firefox's comparative success among end-user-visible FOSS projects stems from the Mozilla Foundation's commitment to product usability. Check out https://firefoxur.github.io