[TASK][FOLLOWUP] Workspaces documentation cleanup

While backporting the manual to TYPO3 7, I found a few
cleanups to do.

Resolves: #77362
Releases: master
Change-Id: I1722685fd8292169506d1258a6c14bd62bd1f057
Reviewed-on: https://review.typo3.org/49327


Reviewed-by: Francois Suter <francois@typo3.org>
Tested-by: Francois Suter <francois@typo3.org>