docs: Introduce a default .readthedocs.yaml

Read The Docs now requires a configuration file, which is awkward when using
RTD to render proposed changes on the list.

Provide the minimal configuration file possible, sacrificing all
reproducibility in order to hopefully not need to touch it moving forwards.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

.readthedocs.yaml

@@ -0,0 +1,18 @@
+# Read the Docs configuration file for Sphinx projects
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+version: 2
+
+build:
+  os: ubuntu-lts-latest
+
+  tools:
+    python: "latest"
+
+  jobs:
+    post_install:
+      # Instead of needing a separate requirements.txt
+      - python -m pip install --upgrade --no-cache-dir sphinx-rtd-theme
+
+sphinx:
+  configuration: docs/conf.py