Replace placeholder text in the http.client module docstring (#121490)

Co-authored-by: Stan Ulbrych <stan@python.org>

Author: samrobbins85

Lib/http/client.py

@@ -1,7 +1,8 @@
 r"""HTTP/1.1 client library
 
-<intro stuff goes here>
-<other stuff, too>
+This module implements the client side of the HTTP and HTTPS protocols.
+HTTPConnection and HTTPSConnection manage a single connection to a server;
+HTTPResponse wraps the reply.
 
 HTTPConnection goes through a number of "states", which define when a client
 may legally make another request or fetch the response for a particular