Where to install a missing firmware during the installation ?

Hi everyone,

I'm struggling to install kali on my computer, indeed i had a firmware missing (rtl_nic/rtl8411) so i put it on a usb disk (which i format before in fat), i created a new repertory in /media named "usb" with mkdir then i tried to mount it with this command mount /dev/sdc1 media/usb and i had a message like "busybox ... multi-call binary", i mounted the usb stick in this usb folder that i created because it saw it on a forum but i guess that i must mount the usb in a special repertory for firmware but i don't know which one it is... please help me :-)

Thanks

Addon