It’s really not that hard. Go to https://www.home-assistant.io/, click on “Getting Started”, scroll down to Installation and follow the (rather simple) 9 steps just as it lays out.
Is that not clear documentation?
As for “no upfront support matrix”, on the Getting Started page there’s links for:
For advanced users (or if you don’t have a device that is supported by this guide), check out our alternative installation methods.
If you click on the first link, you can see the 11 devices supported for the basic installation method. An additional 5 supported VM images, and instructions on how to install it as a VM (these instructions don’t cover all possible contingencies, but as this is an “advanced” install method, the user is expected to have some assumed knowledge).
The second link has additional hardware requirements and performance expectations.
The rest of the stuff (“docker/venv/VM/Supervisor/linux/debian/ubuntu/”) probably isnt for you if you’re just looking to run it on a Pi and don’t understand what the other options are. Those are considered “advanced” methods, and again assume some existing level of knowledge of the user. However the community forum has plenty of threads to read through to get an idea of what each ones is and how it works.
There are additional community guides available for these install methods, including one that has a nice matrix of what you get/loose with each install method.
Then open source projects might not be the best fit; and one that’s still in a beta phase before a 1.0 release (like HA is) especially.
HA is great software, but if you don’t want to worry about updates I fear that you may not enjoy yourself. HA is on a 3(ish) week release cycle, and while the devs do their best to avoid it, there are typically breaking updates in each and every update. That’s something that’s going to be on you to manage and deal with (with the support of the community, obviously), since there’s no tech support phone number to call if/when it stops working.
HA isnt a “fully mature” software product yet. There is a lot of individual learning and maintenance that the users will have to do themselves. Many new features of HA in the past year have worked to cut down on that but we’re not yet at a 1.0 release for a reason, however home automation is inherently a technically complex venture.