Cleanup github.io doc notebook index structure

[jvshields]

@RyanGroneck should take a look at https://tardis-sn.github.io/stardis/possible_stardis_outputs/possible_stardis_outputs.html#Stellar-Model

It seems that basically all of the section headers you used are at the top level of our contents for the result options notebook. Fix that up if you can, and also perhaps make a nested directory where a lot of these example notebooks can be grouped together.