Like others are saying, rootless is there for a reason and should not be disabled. That said if you know what you are doing then you can use the following process:
1.Restart the computer, while booting hold down Command-R to boot into recovery mode.
2.Once booted, navigate to the "Utilities > Terminal" in the top menu bar.
3.Enter csrutil disable in the terminal window and hit the return key.
4.Restart the machine and System Integrity Protection will now be disabled.