Added readthedocs support

.readthedocs.yaml

+# .readthedocs.yaml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Required
+version: 2
+sphinx:
+  configuration: doc/conf.py
+python:
+  version: 3.8
+  install:
+    - requirements: doc/requirements.txt