bpo-38623: Doc: Add section for site module CLI. (GH-17858)

Author: methane

Doc/library/site.rst

@@ -236,6 +236,13 @@ Module contents
  .. versionadded:: 3.2
 
 
+.. _site-commandline:
+
+Command Line Interface
+----------------------
+
+.. program:: site
+
 The :mod:`site` module also provides a way to get the user directories from the
 command line:
 
@@ -244,8 +251,6 @@ command line:
  $ python3 -m site --user-site
  /home/user/.local/lib/python3.3/site-packages
 
-.. program:: site
-
 If it is called without arguments, it will print the contents of
 :data:`sys.path` on the standard output, followed by the value of
 :data:`USER_BASE` and whether the directory exists, then the same thing for