bpo-37741: make importlib.metadata docs discoverable through a module directive. (GH-25415)

Automerge-Triggered-By: GH:jaraco
(cherry picked from commit 23acadc)

Co-authored-by: Jason R. Coombs <[email protected]>

Author: miss-islington

Doc/library/importlib.metadata.rst

@@ -4,6 +4,11 @@
  Using :mod:`!importlib.metadata`
 =================================
 
+.. module:: importlib.metadata
+   :synopsis: The implementation of the importlib metadata.
+
+**Source code:** :source:`Lib/importlib/metadata.py`
+
 .. note::
    This functionality is provisional and may deviate from the usual
    version semantics of the standard library.