readthedocs config: add sphinx configuration key

https://about.readthedocs.com/blog/2024/12/deprecate-config-files-without-sphinx-or-mkdocs-config/
2025-01-20 15:10:03 -08:00 · 2025-01-20 15:10:03 -08:00 · 9e800a4e3c
commit 9e800a4e3c
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@ -14,3 +14,6 @@ python:
   install:
      - requirements: requirements.txt
      - requirements: docs/requirements.txt
+
+sphinx:
+  configuration: docs/conf.py