[CLEANUP] Simplify addStaticFile description

Resolves: #78887
Releases: master, 7.6
Change-Id: Ifb6de078816e851915372d1c5611552fd58f2cce
Reviewed-on: https://review.typo3.org/50885


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Robert van Kammen <rvkammen@hotmail.com>
Tested-by: Robert van Kammen <rvkammen@hotmail.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>