Add citations to PeturbedLJ documentation #123
Description
This pair potential should document that it is the same functional form as Eqs. (3)–(6) of the classic Weeks–Chandler–Andersen paper.
It should also note that it is the same as the ashbaugh potential in azplugins prior to v1. Eq. (1) of Ashbaugh and Hatch is equivalent to the WCA perturbation theory, but folks working in the protein space may know this interaction under that name as a model for hydropathy.