That's actually what we had in chapter 18, "Installation from Source Code on Windows", since removed. But for some reason we decided that on non-Windows platforms, it needed a whole new chapter rather than an extra sentence in the existing one. I think that's massively overkill.
I agree with the premise that we should have a single chapter, in the main documentation flow, named "Installation". It should cover the architectural overview and point people to where they can find the stuff they need to install PostgreSQL in the various ways available to them. I agree with moving the source installation material to the appendix. None of the sections under Installation would then actually detail how to install the software since that isn't something the project itself handles but has delegated to packagers for the vast majority of cases and the source install details are in the appendix for the one "supported" mechanism that most people do not use.