Developer-facing flowchart

[mattwthompson]

Describe the behavior you would like added to Foyer
We have this flowchart for the atom-typing process (from the paper):

since there are a lot of strung-together modular/internal functions that actually implement this algorithm, it would be useful to have this annotated with the functions that implement each step

Describe the solution you'd like
Line numbers would be useful, particularly if tagged to the commit (hitting the y key in GitHub)

Describe alternatives you've considered
Reading internal functions (which is not fun)

Additional context
Add any other context or screenshots about the feature request here.