Update README.md
3.8: update to latest mainline

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
3.8: update to 3.8 final

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
Merge branch '3.8' of git://github.com/beagleboard/kernel into 3.8
not-capebus/pinmux: provide a DT helper for loading pinmux
configs/beaglebone: enable pinmux helper