Use requirements.txt for readthedocs build

Author: nzlosh

.readthedocs.yaml

@@ -17,6 +17,6 @@ sphinx:
 
 # We recommend specifying your dependencies to enable reproducible builds:
 # https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html
-# python:
-#   install:
-#   - requirements: docs/requirements.txt
+python:
+  install:
+    - requirements: docs/requirements.txt