README: Remove list of supported boards and link RN

Add link to Release Notes

Signed-off-by: Daiane Angolini <daiane.angolini@freescale.com>
Remove bblayer.conf
setup-environment will stupidly erase any exitent bblayer.conf
generated from bblayers.conf.sample otherwise
Merge remote-tracking branch 'origin/dora' into dora

Conflicts:
	README