[TASK] Improve config.disableCharsetHeader documentation

Make it clear that config.disableCharsetHeader is about a HTTP header,
not the HTML meta tag.

Releases: master
Resolves: #71687
Change-Id: Ic3f925d02eb6df9ceb8a30e7fe146afa0a309eec
Reviewed-on: https://review.typo3.org/44797


Reviewed-by: Christian Weiske <typo3@cweiske.de>
Tested-by: Christian Weiske <typo3@cweiske.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Harry Glatz <glatz@analog.de>
Tested-by: Harry Glatz <glatz@analog.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>