All Credits to antigad from XDA/4PDA
1) Things you need (i did it with windows 10 x64):
- The recovery file from here
- The flash tool "SP Flash tool" (google gives you the newest version)
- USB Driver for Android/MTK (e.g. from here; there are a few driver-packages in the file; "New inst. win 7&8×64" worked for me; maybe you have to try another one)
- A SuperSu-Installer-Zip (e.g. from attachements)
2) Install the drivers (if you have none installed!); Download the Flashtool and the recovery-file (and unzip it); Inside the zip you will find a scatter-file and revovery.img
3) Start the Flashtool as admin and go to the download window. Click at "Download-Action" and choose the file "MTK_AllInOne_Da.bin" (comes together with the flash tool). Click at "Scatter-loading" and choose "MT6735_Android_scatter.txt" from the unpacked recovery zip. The section below should now be filled with the recovery-file, only the recovery-checkbox should be ticked (otherwise you may loose your smartphone-data)! Choose "Download only" from the dropdown-menu.
4) Connect your phone to the computer (just normal booted, no special recovery- or download-mode). Click at Download in the Flashtool. The application is now ready to install the recovery. Now reboot your phone via the normal power-menu. The Download should start automatically, when the phone reboots. If nothing happens, just try it a second time (sometime windows recognizes a new device very slow 
). When the download was completed sucessfully, a green snag should appear in the flash tool. You can now disconnect your phone.
5) Now lets test your new recovery: Restart you phone holding the power & vol+ buttons. If you have seevral reboots while holding these buttons, you have to release them for a short period of time after the bootscreen appears. A blue screen should appear (you can release the buttons) and you are now entering recovery (maybe you have to allow the recovery to change your system at first). Restart your phone and boot system. Place the SuperSiu-zip at the Sd-Card.
6) Reboot to the recovery holding the above-mentioned combo. Install the SuperSu-Zip in the "install"-menu of the recovery. Reboot normally, you should now have a rooted Cubot X16.