Install mkdocs material when building the documentation site

Author: dgunning

.readthedocs.yaml

@@ -28,6 +28,6 @@ mkdocs:
 # Optional but recommended, declare the Python requirements required
 # to build your documentation
 # See https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html
-# python:
-#    install:
-#    - requirements: docs/requirements.txt
+python:
+  install:
+    - requirements: docs/requirements.txt

docs/requirements.txt

@@ -0,0 +1,2 @@
+mkdocs>=1.5.0
+mkdocs-material>=9.0.0