docs: Ensure literal block rendering

docs: Ensure literal block rendering

Literal block is not rendered as such unless prefixed with two colons
("::") [1].

Sphinx "code-block" directive takes a language name as an argument [2]
and fails if none is supplied.

[1] http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.html#literal-blocks
[2] https://www.sphinx-doc.org/en/master/usage/restructuredtext/directives.html#directive-code-block

Issue-ID: OOM-1612
Change-Id: Ibf5ddf9b50753206b5bcec0df83c8a19346e6ad9
Signed-off-by: Pawel Wieczorek <p.wieczorek2@samsung.com>