[rtd] Add configuration

.readthedocs.yaml

+# SPDX-FileCopyrightText: Copyright © 2023 Idiap Research Institute <contact@idiap.ch>
+#
+# SPDX-License-Identifier: BSD-3-Clause
+
+version: 2
+
+build:
+  os: "ubuntu-22.04"
+  tools:
+    python: "3.10"
+
+python:
+  install:
+    - method: pip
+      path: .
+      extra_requirements:
+        - doc