Adds Hubbard-Kanamori example + small related improvements

[bkesk]

The main contributions are:

1. The Hubbard-Kanamori model example (with no reference to the lattice model builder in afqmctools)
2. Added doc strings to the AutoHFHamiltonian to explain the input parameter conventions
3. fixed an indentation bug in setting the one-body Hamiltonian in AutoHFHamiltonian

[ryanlevy]

Thanks Kyle, good catches! Some nit picky requests but nearly there

[bkesk]

I made changes to the Doc strings in AutoHFHamiltonian in 0e7766a based on your comments @ryanlevy, please confirm that they have been adequately addressed.

I think the only lingering issue here is in the intro to the Hubbard-Kanamori example. See my response to your comment!

[ryanlevy]

Thanks Kyle!