docs: Fix ReadTheDocs sphinx.configuration requirement
Deprecation of projects using Sphinx or MkDocs without an explicit
configuration file:
https://about.readthedocs.com/blog/2024/12/deprecate-config-files-without-sphinx-or-mkdocs-config/
Signed-off-by: Andrei Gherzan <andrei@gherzan.com>
Andrei Gherzan