[BUGFIX] EM does not link to docs.typo3.org

docs.typo3.org is new official documentation platform supporting both
OpenOffice and Sphinx manuals.

Fixes: #52226
Releases: 6.2, 6.1, 6.0
Change-Id: Ie5f27bf15f5174a6e1bb53bedd575ceeb362add8
Reviewed-on: https://review.typo3.org/24017
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers
Reviewed-on: https://review.typo3.org/24053