Update to follow conventions defined in readthedocs docs

Namely: https://docs.readthedocs.io/en/stable/config-file/v2.html

.readthedocs.yml

@@ -1,6 +1,7 @@
 version: 2
+sphinx:
+  configuration: conf.py
 python:
   version: 3
   install:
-      - method: pip
-        path: .
+    - requirements: requirements.txt