statcast_pitcher_spin.md has a typo listing the wrong function.

[ben-gunnels]

The doc currently shows:

statcast_pitcher(start_dt=[yesterday's date], end_dt=None, player_id)

When the doc should show the correct function being described:

statcast_pitcher_spin(start_dt=[yesterday's date], end_dt=None, player_id)

This function name matches the example.

from pybaseball import statcast_pitcher_spin

[MancusoM]

Hey Ben. Great catch. I made https://github.com/jldbc/pybaseball/pull/491 to fix this