doc: add read the docs configuration file

ReadTheDocs documentation build was broken since October, 2023, since file
'.readthedocs.yaml' file is required in the root of the project.

https://onedigi.atlassian.net/browse/XBPL-425

Signed-off-by: Tatiana Leon <Tatiana.Leon@digi.com>

Author: tatianaleon

.readthedocs.yaml

@@ -0,0 +1,34 @@
+# Read the Docs configuration file for Sphinx projects
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Required
+version: 2
+
+# Set the OS, Python version and other tools you might need
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.12"
+    # You can also specify other tool versions:
+    # nodejs: "20"
+    # rust: "1.70"
+    # golang: "1.20"
+
+# Build documentation in the "doc/" directory with Sphinx
+sphinx:
+  configuration: doc/conf.py
+  # Configure Sphinx to use a different builder, for instance use the dirhtml builder for simpler URLs
+  # builder: "dirhtml"
+  # Fail on all warnings to avoid broken references
+  # fail_on_warning: true
+
+# Optionally build your docs in additional formats such as PDF and ePub
+# formats:
+#   - pdf
+#   - epub
+
+# Declare the Python requirements required to build your documentation
+# See https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html
+python:
+  install:
+    - requirements: doc/requirements.txt

doc/requirements.txt

@@ -0,0 +1 @@
+sphinx_rtd_theme