onehot.md in docs should not have subtitle "Batches"

[jessebett]

Given that Building a Language and Compiler for Machine Learning has a section on Automatic Batching it is especially confusing that searching the docs for "batch" returns the section on hot/cold matrix encodings.

I think this section should be renamed to avoid "batch" confusion. Additionally, is automatic batching ready enough to be in the docs?

[darsnack]

As discussed during triage, I will submit a PR to fix this.