Add needed requirements for the sphinx build.

Author: WimDeMeester

readthedocs.yml

@@ -10,6 +10,10 @@ build:
   tools:
     python: "3.11"
 
+python:
+  install:
+    - requirements: docs/requirements.txt
+
 # Build documentation in the "docs/" directory with Sphinx
 sphinx:
   configuration: docs/source/conf.py