add showcase notebook custom for USRSE

[atravitz]

I'm making a separate showcase for USRSE, since the target audience would benefit from a bit more background on why we do RBFEs before we get into it.

Important to Consider

• presentation is 15 minutes + 2-3 for questions.
• the target audience is software research engineers, so I don't need to explain "making software for researchers", but I do need to explain what alchemical free energy calculations are and why they should care. However, I'm not trying to convince this audience that they should try openfe, so much as share how we structure our ecosystem, tooling, and tutorials

TODO:

• add a high-level and concise preamble to explain openfe's purpose
• put CLI first and run through to make sure it's up to date and output is clean
• review the API-level showcase, removing anything that's too in-the-weeds for this audience.

Developers certificate of origin

• I certify that this contribution is covered by the MIT License here and the Developer Certificate of Origin at https://developercertificate.org/.

[review-notebook-app]

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[github-actions]

👈 Launch a binder notebook on branch OpenFreeEnergy/ExampleNotebooks/usrse_showcase

[atravitz]

now lives here https://github.com/OpenFreeEnergy/openfe-usrse-demo/blob/main/README.md