Add section about false sharing problems to documentation

[bennibolm]

False sharing performance issues occurred while thread-parallelizing the bounds checking routine for subcell IDP limiting.
For future referencing, I added a section about the problem and its solution in the documentation.

For more context, see PR #1736 and the experiments and discussions.

[github-actions]

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[ranocha]

Nice idea 👍

[sloede]

Thanks a lot!