RN: Add pointer to kernel linux section

Signed-off-by: Daiane Angolini <daiane.angolini@freescale.com>
RN: Update BSP scope to point external links and Freescale RN

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

Please, help me to add the better pointer for release notes
out of scope of FSL Community BSP but important for
development, such as kernel release notes for linux providers
others that linux-imx.

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

Say it is based on Yocto Project.

Please comment on how to point to YP URL.

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