Add requirements_notebooks.txt to MANIFEST

[jGaboardi]

This PR resolves #343.

xref conda-forge/spopt-feedstock#12 (comment)

[martinfleis]

not a huge fan of this solution of loading all reps from n files on setup (pyproject.toml would be certainly better) but it is fine now.

long-term, none of these should be in manifest as they're not needed in the wheel.

[jGaboardi]

not a huge fan of this solution of loading all reps from n files on setup (pyproject.toml would be certainly better) but it is fine now.

long-term, none of these should be in manifest as they're not needed in the wheel.

FWIW, I agree. After we work the kinks out of using pyproject.toml exclusively (it's causing a headache over in spaghetti) then I'll start pushing for adoption across the PySAL ecosystem.