[TASK] EXT:form - add documentation for #82210

Add the missing breaking rst for issue #82210.

Resolves: #83517
Related: #82210
Releases: master
Change-Id: Id157cf0678912a3008705a1fbb64a2014f2fc3f3
Reviewed-on: https://review.typo3.org/55307


Reviewed-by: Björn Jacob <bjoern.jacob@tritum.de>
Tested-by: Björn Jacob <bjoern.jacob@tritum.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>