Sphinx autobuild no longer auto builds

[doyougnu]

it expects a mutable file system but we've nixified enough that this broke after I bumped the python packages. Will have to use nix to write a script and then set it as a flake target.

[doyougnu]

this works:

I  ~/w/h/hs-opt-handbook.github.io doyougnu/rethinking-tntc• ❱ sphinx-autobuild . _result/html

but you must have the result symlink first from nix, which means you've run nix build.