Add RTD config

.readthedocs.yaml

@@ -0,0 +1,15 @@
+# .readthedocs.yaml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Required
+version: 2
+
+conda:
+  environment: conda_env.yml
+
+sphinx:
+   configuration: docs/conf.py
+
+formats:
+  - pdf