Document parameters given to store_tokens callback

[adamchainz]

Is your feature request related to a problem? Please describe.

I couldn't find this documented anywhere and had to dig into the source to find its arguments

Describe the solution you'd like

Document it in the relevant docstrings and the mentions in the README

Describe alternatives you've considered

n/a

Additional context

n/a

[sujaygarlanka]

@adamchainz Thanks for the feedback! We will look into documenting the callback. Feel free to submit a documentation PR if you have already documented it for yourself and we would love to review and merge it into the SDK.