This is now expected by rtd so I've expanded using their example as
22.04 is one of our supported platforms. I tried to work out if there
was an easy way to re-generate a requirements.txt from our
pythondeps.toml but in the end went for the easier solution.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Cc: qemu-stable@nongnu.org
---
 docs/requirements.txt |  2 ++
 .readthedocs.yml      | 19 ++++++++++++-------
 2 files changed, 14 insertions(+), 7 deletions(-)
 create mode 100644 docs/requirements.txt

diff --git a/docs/requirements.txt b/docs/requirements.txt
new file mode 100644
index 00000000000..691e5218ec7
--- /dev/null
+++ b/docs/requirements.txt
@@ -0,0 +1,2 @@
+sphinx==5.3.0
+sphinx_rtd_theme==1.1.1
diff --git a/.readthedocs.yml b/.readthedocs.yml
index 7fb7b8dd61a..0b262469ce6 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -5,16 +5,21 @@
 # Required
 version: 2
 
+# Set the version of Python 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
 
+# We recommend specifying your dependencies to enable reproducible builds:
+# https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html
+python:
+  install:
+    - requirements: docs/requirements.txt
+
 # We want all the document formats
 formats: all
-
-# For consistency, we require that QEMU's Sphinx extensions
-# run with at least the same minimum version of Python that
-# we require for other Python in our codebase (our conf.py
-# enforces this, and some code needs it.)
-python:
-  version: 3.6
-- 
2.39.2