upgrade rtd to version 2

Author: mmcky

rtd-requirements.txt renamed to docs/rtd-requirements.txt

@@ -1,10 +1,21 @@
-# .readthedocs.yml
+# .readthedocs.yaml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
 
+# Required
+version: 2
+
+# Set the version of Python and other tools you might need
 build:
-  image: latest
+  os: ubuntu-20.04
+  tools:
+    python: "3.9"
 
-python:
-  version: 3.8
-  setup_py_install: true
+# Build documentation in the docs/ directory with Sphinx
+sphinx:
+   configuration: docs/source/conf.py
 
-requirements_file: rtd-requirements.txt
+# Optionally declare the Python requirements required to build your docs
+python:
+   install:
+   - requirements: docs/rtd-requirements.txt