Add value proposition and example to readme.

[kklein]

Checklist

• [ ] Added a CHANGELOG.rst entry

[codecov[bot]]

Codecov Report

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

Project coverage is 95.01%. Comparing base (6b33115) to head (ee6c10a). Report is 42 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #44 +/- ## ======================================= Coverage 95.01% 95.01% ======================================= Files 14 14 Lines 1365 1365 ======================================= Hits 1297 1297 Misses 68 68 ```

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