UG: Add kernel-with-toolchain

Signed-off-by: Lucas Dutra Nunes <ldnunes@ossystems.com.br>
UG: add bad-uglyy-gstreamer-plugins

Signed-off-by: Lucas Dutra Nunes <ldnunes@ossystems.com.br>
UG: add custom-layer

Signed-off-by: Lucas Dutra Nunes <ldnunes@ossystems.com.br>
UG: add a small marker to show where the old user guide starts

Signed-off-by: Lucas Dutra Nunes <ldnunes@ossystems.com.br>