Follow this easy steps
1. Download and install magisk manager apk latest from here (official thread)
2. Download patched boot.img for december security patch frm here
Download patched boot.img for stable january security patch frm here
WIFI ISSUE FIXED
3. Extract patched_boot.img.zip
4. Copy patched_boot.img in fastboot folder.
5. Enable developer option in ur device and enable oem unlocking in developer option.
6. Turn off ur phone.
7. Now press and hold voume down+power button.
8. Now connect your device with PC in fastboot mode
9. Type command
fastboot oem unlock
fastboot boot patched_boot.img
Hit THANKS button if your phone rooted.
Note: If you followed old method to root device just copy this in data folder then use below guide
USE THIS GUIDE WHEN OTA ARRIVES