Explain annotation behavior when used in conjunction with arrows

[zitorelova]

PR Summary

Closes #19084. Added a note in the documentation to describe the behavior of annotations when used with arrows.

PR Checklist

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (run flake8 on changed files to check).
• New features are documented, with examples if plot related.
• Documentation is sphinx and numpydoc compliant (the docs should build without error).
• Conforms to Matplotlib style conventions (install flake8-docstrings and run flake8 --docstring-convention=all).
• New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).

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[jklymak]

Thanks! I think that is helpful...

[tacaswell]

Congratulations on your first Matplotlib PR @zitorelova 🎉

Hopefully we will hear from you again!