User-focused documentation updates

[dotsdl]

Currently, our documentation for stratocaster only gives a brief description of what the library is and how to install it. We want to expand this documentation to give a potential user:

• a clear concept of where stratocaster fits in the OpenFE ecosystem
• a concept document detailing what a Strategy is, what rules they operate under, and how to apply them to an AlchemicalNetwork and any results from that network
• a tutorial showing the application of e.g. ConnectivityStrategy to an AlchemicalNetwork, both with no results yet and some results
• a how-to detailing how a user could write their own Strategy, similar to the how-to for writing gufe Protocols: https://gufe.openfree.energy/en/latest/how-tos/protocol.html