doc: use docker to build documentation

docker (container) is another way to build the documentation and fortunately
there is already a docker image (sphinxdoc/sphinx) with sphinx so we can use
it to generate the documentation.

Change-Id: I33fba6c5e4810e20546559c80a8f2eecabd4c123
Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
1 file changed