[TASK] Include new Extension Manual

Releases: 6.2
Resolves: #57853
Change-Id: Ib358dfea1960710a2be5830e738d00d7778fd720
Reviewed-on: https://review.typo3.org/29457
Reviewed-by: Francois Suter
Tested-by: Francois Suter
Reviewed-by: Nico de Haen
Tested-by: Nico de Haen