fsl-userspace-pkg: Fix  FSL userspace pkg description

Signed-off-by: Daiane Angolini <daiane.angolini@freescale.com>
userspace-pkg: Add a chapter for userspace packages

Add a chapter for few highlighted userspace packages
from Yocto.

Signed-off-by: Daiane Angolini <daiane.angolini@freescale.com>
known-issues: Add two known issues

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