docs: Add snippet for python module path method [skip ci]

Which somehow wasn't included in the original pull request.

docs/markdown/snippets/python-path-method.md

@@ -0,0 +1,5 @@
+## Added a .path() method to object return by python.find_installation()
+
+`ExternalProgram` objects as well as the object returned by the
+`python3` module provide this method, but the new python module did
+not.