Update documentation build

Author: cthoyt

.readthedocs.yml

@@ -0,0 +1,8 @@
+# See: https://docs.readthedocs.io/en/latest/yaml-config.html
+build:
+    image: latest
+python:
+  version: 3.6
+  pip_install: true
+  extra_requirements:
+  - docs

tox.ini

@@ -70,10 +70,8 @@ description = Run the pyroma tool to check the project's package friendliness.
 
 [testenv:docs]
 changedir = docs
-deps =
-    sphinx
-    sphinx-rtd-theme
-    sphinx-autodoc-typehints
+extras =
+    docs
 commands =
     mkdir -p {envtmpdir}
     cp -r source {envtmpdir}/source