docs: Fix RtD build
docs: Fix RtD build

Markdown parser has changed[1].

[1] https://docs.readthedocs.io/en/stable/intro/getting-started-with-sphinx.html#using-markdown-with-sphinx

Signed-off-by: Andrei Gherzan <8dc7c09356db0b1762fb140617d7375c0a5a4131@gherzan.com>

agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi