Need better figures for nonorthogonal grid generation documentation

[mikekryjak]

There is already a figure that demonstrates the settings for divertor region nonorthogonal grid generation, but I found it very opaque to understand how it's generated above the X-point and the PFR. I think this benefit from a nice figure and some more words. I think I understand what's going on now thanks to @johnomotani's help and I'm happy to create one. I don't think I'll be able to do it before I go on leave but I'm leaving this here and will get back to it.