add zonal_stats guide, update docs

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (e86d3ec) 99.27% compared to head (65f9060) 99.27%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #57 +/- ## ======================================= Coverage 99.27% 99.27% ======================================= Files 4 4 Lines 416 416 ======================================= Hits 413 413 Misses 3 3 ```

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