[3.15] Replace placeholder text in the http.client module docstring (GH-121490) (#160969)

(cherry picked from commit 4a9b981)

Co-authored-by: Sam Robbins <samrobbinsgb@gmail.com>
Co-authored-by: Stan Ulbrych <stan@python.org>

Author: 3 people

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