docs: add the readthedocs configuration

We need to install additional plantuml package before the build

Fixes: https://pagure.io/freeipa/issue/9148

Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
Reviewed-By: Francisco Trivino <ftrivino@redhat.com>

.readthedocs.yaml

@@ -0,0 +1,30 @@
+# .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-20.04
+  tools:
+    python: "3.8"
+  apt_packages:
+    - plantuml
+    - graphviz
+    - fonts-ipafont
+    - fonts-ipaexfont
+
+# Build documentation in the doc/ directory with Sphinx
+sphinx:
+   configuration: doc/conf.py
+
+# If using Sphinx, optionally build your docs in additional formats such as PDF
+# formats:
+#    - pdf
+
+# Optionally declare the Python requirements required to build your docs
+python:
+   install:
+   - requirements: doc/requirements.txt