cmsis: Initial commit of license and readme from 5.6.0

Include the first 2 files in order to avoid having an empty repository.

Origin: CMSIS_5
License: Apache-2.0
URL: https://github.com/ARM-software/CMSIS_5/tree/5.6.0


commit: b5f0603d6a584d1724d952fd8b0737458b90d62b
Purpose: Provide a hardware interface to the Arm architecture
Maintained-by: External

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>