docs: add rtd

Author: tlambert03

.readthedocs.yaml

@@ -0,0 +1,19 @@
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+version: 2
+
+build:
+  os: ubuntu-20.04
+  tools:
+    python: "3.10"
+
+mkdocs:
+  configuration: mkdocs.yml
+  fail_on_warning: true
+
+python:
+  install:
+    - method: pip
+      path: .
+      extra_requirements:
+        - docs