Hi all with the < waiting for any device > issue in step 6 of “Unlocking the bootloader”: I had the same issue and using another USB cable did not resolve it.
For me the issue was that I had to run the fastboot commands as root. i.e. sudo fastboot ... in Linux
→ if you have the same issue in Linux, make sure to make yourself su during the installation, as there are a lot of fastboot commands and it would be a pain to add sudo before all of them → enter sudo su in the terminal before using the first fastboot command.
Kodus to @Lidwien who figured this out here 
@Manoj : this should probably be mentioned in the installation instructions!