doc: add read the docs configuration file

As announced on https://blog.readthedocs.com/migrate-configuration-v2/,
having a .readthedocs.yaml file at the root of the project becomes
mandatory.

.gitattributes

@@ -6,6 +6,7 @@ version.inc.in export-subst
 .gitattributes export-ignore
 init/.gitignore export-ignore
 .cirrus.yml export-ignore
+.readthedocs.yaml export-ignore
 codecov.yml export-ignore
 script/mb export-ignore
 script/mlprof export-ignore

.readthedocs.yaml

@@ -0,0 +1,24 @@
+# .readthedocs.yaml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Required
+version: 2
+
+# Set the version of Python and other tools you might need
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.11"
+    # You can also specify other tool versions:
+    # nodejs: "19"
+    # rust: "1.64"
+    # golang: "1.19"
+
+# Build documentation in the docs/ directory with Sphinx
+sphinx:
+   configuration: doc/source/conf.py
+
+# If using Sphinx, optionally build your docs in additional formats such as PDF
+# formats:
+#    - pdf