RN: Update BSP scope to point external links and Freescale RN

The Release Notes for the kernel is out of scope of this RN.

Signed-off-by: Daiane Angolini <daiane.angolini@freescale.com>
RN: Add the Release Schedule section

Say it is based on Yocto Project.

Signed-off-by: Daiane Angolini <daiane.angolini@freescale.com>