Add appropriate acknowledgements to PERSES and openmmtools contributors

Since significant chunks of the code (~thousands of lines) in this repo are copy-pasted from https://github.com/choderalab/perses (and some bits from https://github.com/choderalab/openmmtools), which constitutes a ton of hard work from graduate students and software engineers not directly a part of OpenFE, I strongly think that more effort should be put into acknowledging these efforts. In particular, I think it would be appropriate to include:

Chodera Lab PhD Students & Post-docs:
@zhang-ivy
@dominicrufa
@andrrizzi
@Lnaden
@hannahbrucemacdonald
@pgrinaway

Software Scientists:
@ijpulidos
@mikemhenry

At a minimum, putting on the "front page" that this work is indebted to both of those code bases would be a step in the right direction. (edited for friendliness)

Thanks!