Add sudo instructions

README.md

@@ -12,10 +12,22 @@ Backlight utility for Linux
 
 ```bash
 go get gitlab.com/tslocum/brightness
+cp ~/go/bin/brightness /sbin/brightness
+sudo visudo
 ```
 
+Add the following line to your sudoers file to use `brightness` without entering a password:
+
+```
+%wheel ALL=(ALL) NOPASSWD: /sbin/brightness
+```
+
+You may need to modify `%wheel` to match the superuser group of your system.
+
 ## Usage
 
+`sudo` is required to modify brightness. It is omitted below for clarity.
+
 ### Set
 
 ```bash