A few more details, but the process is pretty straightforward. Most people have problems with Windows drivers more than anything else. And you need adb and fastboot, which are generally part of the Android SDK but you can get them separately.
adb push LATEST supersu.zip to device while in ROM
adb reboot bootloader (boot into the bootloader)
fastboot oem unlock (unlock the bootloader)
fastboot reboot-bootloader (reboot back into the now-unlocked bootloader)
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