chore: add readthedocs config (#220)

https://blog.readthedocs.com/migrate-configuration-v2/

The new config allow us to specify the package requirements of the docs,
this should fix the build process at readthedocs.

Author: jooola

.readthedocs.yaml

@@ -0,0 +1,26 @@
+---
+# Read the Docs configuration file for Sphinx projects
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Required
+version: 2
+
+# Set the OS, Python version and other tools you might need
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.11"
+
+# Build documentation in the "docs/" directory with Sphinx
+sphinx:
+  configuration: docs/conf.py
+
+# Optionally build your docs in additional formats such as PDF and ePub
+formats: [pdf, epub]
+
+# See https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html
+python:
+  install:
+    - method: pip
+      path: .
+      extra_requirements: [docs]