[TASK] Add documentation for removal of BigDocumentTemplate
This patch adds the missing documentation for the breaking change of
removing the class BigDocumentTemplate without deprecation.
Releases: 7.6
Resolves: #75942
Related: #63441
Related: #45955
Change-Id: I8bc7e2674da8c2abba1698a3a7c5fd8bf62c41b3
Reviewed-on: https://review.typo3.org/47931
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>