DOC: include Offset.__call__ to autosummary to fix sphinx warning
@datapythonista is this the right way to fix the doc build? I'm not sure, sphinx still confuses me with those. @jorisvandenbossche knows better. It clearly fixes it, because CI is green ;)

Now, the actual answer: it depends. Are we fine with including the `__call__` docstring? Is this considered public / documented in the user guide? > It clearly fixes it, because CI is green ;)
> 
> Now, the actual answer: it depends. Are we fine with including the `__call__` docstring? Is this considered public / documented in the user guide?

these *are* public methods. Then the fix is fine Thanks @jbrockmendel ! @Meeseeksdev backport to 1.0.x

