add docs/requirements.txt to .readthedocs.yaml

Author: lfagundes

.readthedocs.yml

@@ -27,6 +27,6 @@ sphinx:
 # Optional but recommended, declare the Python requirements required
 # to build your documentation
 # See https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html
-# python:
-#    install:
-#    - requirements: docs/requirements.txt
+python:
+    install:
+    - requirements: docs/requirements.txt