1. Install JDK and Android SDK for adb
2. Install heimdall. However the classic one doesn't install. Had to use Heimdall-1.4.1-Unofficial-Signed.dmg
3. Go into Download Mode (Vol Down + Power + Home Key) with no wires connected. After you are in the loading screen, connect USB wire to computer and install recovery image (from TWRP).
4. Install TWRP 3.0.2-0 using heimdall as per command: heimdall flash --RECOVERY ~/Downloads/Cyanogenmod/Samsung\ S4/twrp-3.0.2-0-jfltetmo.img --no-reboot
5. In case that doesn't work, try OUDHS-Recovery-jfltetmo-188.8.131.52-recovery.img. However, this is sticky. When using the OUDHS-Recovery-jfltetmo-184.108.40.206-recovery.img, it screws up the booting in a way that no other recovery image (TWRP, CWM, etc.) can fix it. The best way to fix it is to use OUDHS-Recovery-Installer-Premia-4G-220.127.116.11-2.img and then use twrp-3.0.2-0-jfltetmo.img in sequence. This allows TWRP to run without issues
6. On your SD card, copy "cm-13.0-20160417-NIGHTLY-jfltetmo.zip" and "open_gapps-arm-6.0-pico-20160417.zip".
7. Load the phone into Recovery Mode (Vol Up + Power + Home Key). TWRP allows you to install multiple zips (up to 10). Install both the zips from #6 by selecting them in order (CM first).
8. Reboot your phone and welcome to Cyanogenmod 13 (Android 6.0.1) on your Samsung Galaxy S4 (SGH-M919)