UG: add download section

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

Signed-off-by: Lucas Dutra Nunes <ldnunes@ossystems.com.br>
UG: add build-result page

Signed-off-by: Lucas Dutra Nunes <ldnunes@ossystems.com.br>
UG: fix code-blocks with invalid banch substitutions

Unfortunatelly SphinxDocs still doesn't do nested directives, so it
can't add a code block with a replacement token in it. So it has to be
hardcoded, for now.

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

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

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

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

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