docs: update docstring to point to actual create_arifact_cache

This was moved out of pants.cache with 27f01c43. An option is
maybe take the hardcoded path out, since they sometimes age poorly.

Testing Done:
Just a docstring change, but I ran the CI so this section wouldn't be blank. CI SUCCESS.

Reviewed at https://rbcommons.com/s/twitter/r/438/