I setup Tails on a sandisk 16 gb but it doesnt show up when I hold option on reboot, I only see my mac drive. Is this to do with the non-removability of the sandisk, is there a way to fix this? I tried installing refind but when I booted up i wasnt given a linux boot option. I'm very new to this process and dont really understand using terminal and the like. Would really appreciate any possible help.