Add intersphinx extension.

Author: tkem

docs/conf.py

@@ -26,8 +26,10 @@ def get_version():
     "sphinx.ext.autodoc",
     "sphinx.ext.coverage",
     "sphinx.ext.doctest",
+    "sphinx.ext.intersphinx",
     "sphinx.ext.todo",
 ]
 exclude_patterns = ["_build"]
 master_doc = "index"
 html_theme = "classic"
+intersphinx_mapping = {"python": ("https://docs.python.org/3", None)}