Add docs about converting between shapely and cf

[jsignell]

I finally got around to taking a crack at #497. Feel free to add anything.

[codecov[bot]]

Codecov Report

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

Project coverage is 85.56%. Comparing base (a9cebee) to head (792def4). Report is 10 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #512 +/- ## ========================================== - Coverage 85.78% 85.56% -0.23% ========================================== Files 13 13 Lines 2364 2376 +12 Branches 183 187 +4 ========================================== + Hits 2028 2033 +5 - Misses 303 310 +7 Partials 33 33 ``` | [Flag](https://app.codecov.io/gh/xarray-contrib/cf-xarray/pull/512/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xarray-contrib) | Coverage Δ | | |---|---|---| | [mypy](https://app.codecov.io/gh/xarray-contrib/cf-xarray/pull/512/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xarray-contrib) | `38.27% <ø> (-0.26%)` | :arrow_down: | | [unittests](https://app.codecov.io/gh/xarray-contrib/cf-xarray/pull/512/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xarray-contrib) | `93.89% <ø> (-0.10%)` | :arrow_down: | 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=xarray-contrib#carryforward-flags-in-the-pull-request-comment) to find out more.

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[jsignell]

Not really sure how coverage can go down on a pure docs PR 😅

[dcherian]

Thanks. Great improvement over an empty page :D

[jsignell]

Now there is a page about points :)