Welcome to the SuperSU root beta download page. You will be able to download latest SuperSU root beta version from this webpage. SuperSU root beta version initially released on 02/04/2015 and it was the SuperSU beta v2.47. SuperSU systemless root still in the beta version and there are various bugs.
At this moment, latest SuperSU beta is v2.67. Chainfire mentioned, he has been tested this on various Samsung devices which running Android 4.3 to 5.1 and recent Nexus devices which running Android 6.0.
If you are coming from SuperSU install, you must re flash the stock system partition before install this. If you are coming from SuperSU beta 2.60 system less install, then you can flash the ZIP without any special instruction.
If TWRP ask you to keep / system read only. Without any doubt, just keep it read only.
If TWRP inform you SuperSU is not installed on your device and ask you to install it. Do not install it. If you install it will break things.
Specially, thank you Chainfire for your Android development tools. Thanks XDA for the huge contribution for the Android community.