add rtd yaml v2

Author: ahsan-z-khan

.readthedocs.yml renamed to .readthedocs.yaml

@@ -4,13 +4,19 @@
 
 version: 2
 
+build:
+  os: ubuntu-20.04
+  tools:
+    python: "3.9"
+
+
 python:
-  version: 3.9
   install:
     - method: pip
       path: .
     - requirements: doc/requirements.txt
 
+
 sphinx:
   configuration: doc/conf.py
   fail_on_warning: true # http://www.sphinx-doc.org/en/master/man/sphinx-build.html#id6