bpo-30535: Explicitly note that sys.meta_path is not empty

Author: Windsooon

Doc/library/sys.rst

@@ -926,7 +926,8 @@ always available.
 
     A list of :term:`meta path finder` objects that have their
     :meth:`~importlib.abc.MetaPathFinder.find_spec` methods called to see if one
-    of the objects can find the module to be imported. The
+    of the objects can find the module to be imported. By default, it holds entries
+    to handle the standard kinds of modules (.py files, extension modules...). The
     :meth:`~importlib.abc.MetaPathFinder.find_spec` method is called with at
     least the absolute name of the module being imported. If the module to be
     imported is contained in a package, then the parent package's :attr:`__path__`