How To Disable/Enable SIP on Mac OS X 10.11 El Capitan

Apple added SIP (System Integrity Protection) in OS X El Capitan. SIP is a blockade on editing the /System, /sbin, and /usr directories (with the exception of the /usr/local subdirectory).
System Integrity Protection is a security technology in OS X El Capitan that's designed to help prevent potentially malicious software from modifying protected files and folders on your Mac.

In OS X, the “root” user account previously had no permission restrictions and could access any system folder or application on your Mac. Software gained root-level access when you entered your administrator name and password to install it and could then modify or overwrite any system file or application.

System Integrity Protection restricts the root account and limits the actions that the root user can perform on protected parts of OS X.
 
Disabling SIP

How To Disable/Enable SIP on Mac OS X 10.11 El Capitan