add pointer to xamr repo (#4560)

## Summary

## Additional background

## Checklist

The proposed changes:
- [ ] fix a bug or incorrect behavior in AMReX
- [ ] add new capabilities to AMReX
- [ ] changes answers in the test suite to more than roundoff level
- [ ] are likely to significantly affect the results of downstream AMReX
users
- [x] include documentation in the code and/or rst files, if appropriate

Author: asalmgren

Docs/sphinx_documentation/source/Visualization.rst

@@ -543,6 +543,10 @@ HPC facility for high-throughput visualization of large data sets.
 
 Note - AMReX datasets require yt version 3.4 or greater.
 
+We also note that there is active development of an xarray-like interface
+for AMReX simulation data via yt; see the `xamr docs <https://xamr.readthedocs.io/>`_
+for more details.
+
 Using on a local workstation
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