Add readthedocs config file

Signed-off-by: Håkon Wiik Ånes <hwaanes@gmail.com>

readthedocs.yml

@@ -0,0 +1,22 @@
+# .readthedocs.yml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Required
+version: 2
+
+# Build documentation in the doc/ directory with Sphinx
+sphinx:
+  configuration: doc/conf.py
+
+# Build doc in all formats (HTML, PDF and ePub)
+formats: all
+
+# Python environment for building the docs
+python:
+  version: 3.8
+  install:
+    - method: pip
+      path: .
+      extra_requirements:
+        - doc