The latest release of this Mathlib manual can be read here.
This is mostly adapted code from the Lean Language Reference. You should check there for installation instructions.
Any problems beyond the content itself are probably carried over from there, and might need fixing there.
To build the manual, run the following command:
lake exe generate-manual --depth 2
Then run a local web server on its output:
python3 -m http.server 8880 --directory _out/html-multi
Then open http://localhost:8880 in your browser.
In theory, one should be able to update this by calling a simple
lake update
However, this requires Verso to be compatible with the Lean version Mathlib uses.
We happily accept content!