Add sphinx-rtd-theme to docs

First implementation

.readthedocs.yaml

@@ -22,6 +22,7 @@ sphinx:
 # 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
+    - sphinx-rtd-theme

pyproject.toml

@@ -34,7 +34,7 @@ classifiers = [
 requires-python = ">=3.8"
 dependencies = ["django>=4.2"]
 [project.optional-dependencies]
-docs = ["sphinx"]
+docs = ["sphinx", "sphinx-rtd-theme"]
 
 [project.urls]
 Homepage = "http://github.com/django-waffle/django-waffle"