Fix the docs building requirements

Author: matthiask

.readthedocs.yaml

@@ -10,8 +10,10 @@ build:
 
 sphinx:
   configuration: docs/conf.py
-# python:
-#   install:
-#     - requirements: docs/requirements.txt
-#     - method: pip
-#       path: .
+
+python:
+  install:
+    - method: pip
+      path: .
+      extra_requirements:
+        - docs