Add the minimum USB size required in the system requirement page
A user reported not seeing that Tails needed at least an 8Gb USB stick
until being in the middle of the installation process.
It seems that we only specify that in the overview pages of the installation guide, and, I think it would be great to say it as well in https://tails.boum.org/doc/about/requirements
Feature Branch: doc/16810-usb-size-in-requirements
- Blocks #16711 (closed)