[TASK] Suggest "fileinfo" PHP extension

While not exactly mandatory this extension is essential for a fully
working TYPO3 installation, thus recommend to install it.

Resolves: #77153
Releases: master, 7.6
Change-Id: Ifa88653e36a86771b7549f953a019d2cee0bd367
Reviewed-on: https://review.typo3.org/49049


Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Tested-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>