Update import command in quickstart documentation

[grallc]

updated import parameter to match https://github.com/dyc3/steamguard-cli/blob/master/src/commands/import.rs

running the import command with --sda does not work:

error: unexpected argument '--sda' found

Usage: steamguard import [OPTIONS]

For more information, try '--help'.

we can see in import.rs the correct flag is --files

[dyc3]

Good catch, thank you!