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: I06b0621cd7509a8279655e828680b92241b9fde4
Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
1 file changed