update kernel version

INSTALL.md

 # Ubuntu - Binary
 
-Install a 4.2+ kernel from http://kernel.ubuntu.com/~kernel-ppa/mainline,
+Install a 4.3+ kernel from http://kernel.ubuntu.com/~kernel-ppa/mainline,
 for example:
 
 ```bash
-VER=4.2.0-999
-REL=201509072200
-PREFIX=http://kernel.ubuntu.com/~kernel-ppa/mainline/daily/2015-09-08-unstable/
+VER=4.3.0-999
+PREFIX=http://kernel.ubuntu.com/~kernel-ppa/mainline/daily/2015-09-21-unstable/
+REL=201509202159
 wget ${PREFIX}/linux-headers-${VER}-generic_${VER}.${REL}_amd64.deb
 wget ${PREFIX}/linux-headers-${VER}_${VER}.${REL}_all.deb
 wget ${PREFIX}/linux-image-${VER}-generic_${VER}.${REL}_amd64.deb
@@ -14,6 +14,8 @@ sudo dpkg -i linux-*${VER}.${REL}*.deb
 # reboot
 ```
 
+Update PREFIX to the latest date, and you can browse the files in the PREFIX url to find the REL number.
+
 Tagged bcc binary packages are built for Ubuntu Trusty (14.04) and hosted at
 http://52.8.15.63/apt/.