Update readthedocs.yml

Update per new requirements: https://about.readthedocs.com/blog/2024/12/deprecate-config-files-without-sphinx-or-mkdocs-config/

Author: davidwagner

readthedocs.yml

@@ -7,6 +7,9 @@ build:
   tools:
     python: "3.6"
 
+sphinx:
+  configuration: docs/conf.py
+
 conda:
   environment: linux_environment.yml