Minor docs cleanup

[esoteric-ephemera]

Correcting out of date info / incorrect links in the docs:

• Should close #1043, wherein the VASP workflows link to makers in other code bases
• Some out of date OpenMM info - @orionarcher can you double check my changes are right? The docs were pointing to your branch for install info

[JaGeo]

@esoteric-ephemera Thank you very much! 😀

[JaGeo]

Waiting for @orionarcher to confirm before merging.

[orionarcher]

LGTM

[janosh]

thanks @esoteric-ephemera! 👍