Improved Tutorials

[PaulWAyers]

We should add some improved tutorials for the most common use cases, including plain-vanilla Richardson-Gaudin and the picket-fence Richardson-Gaudin model.

[RichRick1]

We can do that! @PaulWAyers do you have any interesting property of the hamiltonian (like energy limit in case of infinite lattice, etc) we can show in the tutorial?

[PaulWAyers]

There are some phase transitions that one can see as a function of the pair-interaction strength, $g$. The issue with Richardson is that the (easy) way to solve it using a CI code is incredibly inefficient compared to the "right" way to solve it (pseudoanalytically). Perhaps just showing that the wavefunction becomes very far from single-reference for sufficiently large systems, $|\braket{\Psi(0)|\Psi(g)}| \rightarrow 0$ is already interesting.