docs: Add intersphinx mappings

Author: ales-erjavec

doc/development/source/conf.py

@@ -370,4 +370,7 @@
 
 
 # Example configuration for intersphinx: refer to the Python standard library.
-intersphinx_mapping = {'https://docs.python.org/3/': None}
+intersphinx_mapping = {
+    'https://docs.python.org/3/': None,
+    'https://orange-widget-base.readthedocs.io/en/latest/': None,
+}