[BUGFIX] sysext:core Documentation reST syntax

Change-Id: I9b14fb1dfb13a6ec673096845a5e23dbd1a204da
Resolves: #71258
Releases: 7
Reviewed-on: https://review.typo3.org/44487


Reviewed-by: Martin Bless <m.bless@gmx.de>
Tested-by: Martin Bless <m.bless@gmx.de>
Reviewed-by: Daniel Siepmann <daniel.siepmann@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>