Add .readthedocs.yaml to specify legacy RTD build container

.readthedocs.yaml
- Now use one of the legacy build containers to avoid issues
  with RTD builds.

Signed-off-by: Bob Yantosca <yantosca@seas.harvard.edu>

.readthedocs.yaml

@@ -0,0 +1,47 @@
+# .readthedocs.yaml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+#
+# NOTE: This is now needed in order to prevent builds from failing due
+# to Python package issues at the ReadTheDocs site. For more info, see:
+# https://github.com/readthedocs/readthedocs.org/issues/10290
+#   -- Bob Yantosca (10 May 2023)
+
+# Required
+version: 2
+
+## Set the version of Python and other tools you might need
+#build:
+#  os: ubuntu-22.04
+#  tools:
+#    python: "3.7"
+#    # You can also specify other tool versions:
+#    #nodejs: "19"
+#    #rust: "1.64"
+#    #golang: "1.19"
+
+
+# Use the legacy image to avoid issues with older python packages
+#  -- Bob Yantosca (11 May 2023)
+# Set the version of Python and other tools you might need
+build:
+  image: latest
+  apt_packages:
+    - libclang
+    - cmake
+python:
+  version: "3.7"
+
+# Build documentation in the docs/ directory with Sphinx
+sphinx:
+  builder: html
+  configuration: docs/source/conf.py
+
+# If using Sphinx, optionally build your docs in additional formats such as PDF
+#formats:
+#  - pdf
+
+# Optionally declare the Python requirements required to build your docs
+python:
+  install:
+  - requirements: docs/requirements.txt