Document path_or_zarr

[codecov[bot]]

Codecov Report

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

Project coverage is 93.15%. Comparing base (e542f7c) to head (c5ed97b). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #974 +/- ## ======================================= Coverage 93.15% 93.15% ======================================= Files 18 18 Lines 6368 6368 Branches 1142 1142 ======================================= Hits 5932 5932 Misses 296 296 Partials 140 140 ``` | [Flag](https://app.codecov.io/gh/tskit-dev/tsinfer/pull/974/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev) | Coverage Δ | | |---|---|---| | [C](https://app.codecov.io/gh/tskit-dev/tsinfer/pull/974/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev) | `93.15% <ø> (ø)` | | | [python](https://app.codecov.io/gh/tskit-dev/tsinfer/pull/974/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev) | `95.50% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev#carryforward-flags-in-the-pull-request-comment) to find out more.

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