doc: fs: Add information on samples that utilize VFS
doc: fs: Add information on samples that utilize VFS

There are several interesting use caseis of VFS scattered around
in samples, for example usage of FAT in RAM in USB mass storage
that are worth mentioning in VFS reference documentation.

Signed-off-by: Dominik Ermel <1a1d45a9cc0c98a37f8d0a0d2dbe3cacc0b2344f@nordicsemi.no>

galak/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,Vudentz/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,nashif/zephyr,nashif/zephyr,nashif/zephyr,galak/zephyr,Vudentz/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr