*copy the links and paste them in the search bar of the browser, because I don't have the minimum of 10 posts to use clickable links on my posts*
Video: youtu.be/oWnkta-srnA
Preparation: After you downloaded those files, move "Flashable SuperSU.zip" in your SD Card or in internal memory. Extract your scatter from your original firmware of the phone named as "MT6580_Android_scatter.txt" and put it together with TWRP recovery renamed as "recovery.img", in a separate folder.
Flashing TWRP recovery: Open SP Flash Tool, load scatter from that folder and you will see only recovery is checked. Press Download button and then, plug USB cable into the phone without battery. When download is complete, unplug the USB cable, put the battery back and turn on the phone into recovery mode, by pressing Volume Up button and Power button at the same time. The recovery will work only if you plug in a USB mouse into your phone. Maybe we can get a solution from hovatek for this. After you plug in the mouse, the cursor will show up.
Installing SuperSU: Allow modifications, select "Install", select your storage (by default is showing up internal memory) and select "Flashable SuperSU.zip". Swipe to install and wait until is done. When is done, press "Reboot System" and wait for phone to boot up. After the boot is complete, SuperSU will show up in the aplications list.
Observations:
In the video, my phone has Android 5 (I prefere 5 more than 6, because is too buggy) but you have Android 6, so when installation of SuperSU is done, TWRP will ask if you want to install SuperSU, so choose do not install, because you already did it.
Do not update SuperSU to the last version! May cause optimization to all apps after every reboot.