[docs] find new home for `OpenFE_showcase_1_RBFE_of_T4lysozyme.ipynb` example

[mikemhenry]

In fixng this issue https://github.com/OpenFreeEnergy/openfe/issues/843 here https://github.com/OpenFreeEnergy/openfe/pull/733 I realized that we need to update the showcase to point to our new one.

This means we need a new home for OpenFE_showcase_1_RBFE_of_T4lysozyme.ipynb which was moved in this commit https://github.com/OpenFreeEnergy/openfe/pull/733/commits/ba477017bb47e1bf65f0c261326bf7b42ee3faa4