Docs for kwargs in shift function

## Issue Description

The docs for the shift function could be clearer. While the examples give you a rough idea what kwargs are accepted it would be nice with a complete list of accepted kwargs without poking through the code too much.

Start by finding the shift function's documentation and implementation, then compare the existing examples with the kwargs accepted by the function. Done means the documentation includes a complete, accurate list of accepted kwargs without requiring readers to inspect the code.

Written by the indexing model from the issue text.