Summary

This improves the documentation of OverrideSync, based on an exchange between @WeiqunZhang, @aeriforme, and myself in BLAST-WarpX/warpx#6438:

• Add @WeiqunZhang's example in Poisson Solver: Synchronize nodal data before solve BLAST-WarpX/warpx#6438 (comment) to the docstring of FabArray::OverrideSync in Src/Base/AMReX_FabArray.H.
• Copy docstring of FabArray::OverrideSync over to docstring of MultiFab::OverrideSync in Src/Base/AMReX_MultiFab.H for consistency.
• Add @WeiqunZhang's comment in Poisson Solver: Synchronize nodal data before solve BLAST-WarpX/warpx#6438 (comment) to the documentation in Docs/sphinx_documentation/source/Basics.rst, highlighting the difference between the two ways of synchronizing the data with owners overriding non-owners.

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
• include documentation in the code and/or rst files, if appropriate