Improve error message when the USB stick is too small

The current message is:

Sorry, this device is too small to run Tails. Please use a device with at least 8 GiB. Press ENTER to shut down.

Thanks to a report sent to help desk, we learned that it's unclear whether 8 GiB relates to the USB stick or the RAM on the computer.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information