Docs: Enable move to RTD

Add .reathedocs.yaml file which is used to build the documentation.
Edit docs/conf.py to avoid KeyError on RTD builds.

Change-Id: Idbe7f98e5333a82b92dbedd5a43696fe55fd1ed4
Signed-off-by: Elena Uziunaite <elena.uziunaite@arm.com>
diff --git a/.readthedocs.yaml b/.readthedocs.yaml
new file mode 100644
index 0000000..ae6b72e
--- /dev/null
+++ b/.readthedocs.yaml
@@ -0,0 +1,34 @@
+#-------------------------------------------------------------------------------
+#
+# Copyright (c) 2023, Arm Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+#-------------------------------------------------------------------------------
+
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Version of the configuration file, v1 is no longer supported
+version: 2
+
+# Configuration for the documentation build
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.11"
+  apt_packages:
+    - plantuml
+
+# Build documentation in the "docs/" directory with Sphinx
+sphinx:
+  configuration: docs/conf.py
+
+# The documentation will also be built in a pdf format
+ formats:
+    - pdf
+
+# Configuration of the Python environment
+python:
+   install:
+   - requirements: docs/requirements.txt