[TASK] CSH manual: differentiate copyright notice from help content

Improve visual differentiation of content and copyright notice.
A visual hruler is added. Font-size and color is slightly adopted.

Resolves: #79895
Releases: master
Change-Id: Idd7190d860c6083d3333b82dba9a796a0bce0e2c
Reviewed-on: https://review.typo3.org/51746


Tested-by: TYPO3com <no-reply@typo3.com>
Tested-by: Riccardo De Contardi <erredeco@gmail.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>