You can also use a package that make things quite a bit easier... (found on another forum)
it's called Combo_TWRP3_IDOV2 .zip (as i can't post link you'll have to found it yourself...)
you'll also need to install the adb drivers first (search for the universal adb drivers ...)
your phone needs to be unlocked, but don't need to be rooted yet.
-clean existing drivers, then Install ADB drivers.
-launch your RM3 in fastboot mode
-Connect your phone, wait a few seconds then launch twrp-3.0.2-0-ido .bat (which is in Combo_TWRP3_IDOV2).
-follow the steps, press Enter. then the phone will restart under TWRP Recovery
-choose the language.
If you've put a ROM and/or superSU on your phone, you can then install them.