[3.15] gh-90982: Document prefixes argument on site.getsitepackages (GH-31546) (#155643)

Co-authored-by: Addison Snelling <addison@asnell.io>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Author: 4 people

Doc/library/site.rst

@@ -449,12 +449,19 @@ Module contents
       Also processes :file:`.start` files.  See :ref:`site-start-files`.
 
 
-.. function:: getsitepackages()
+.. function:: getsitepackages(prefixes=None)
 
    Return a list containing all global site-packages directories.
 
+   For each directory present in *prefixes* (or :data:`PREFIXES` if *prefixes*
+   is ``None``), this function will find its site-packages subdirectory
+   depending on the system environment, and will return a list of full paths.
+
    .. versionadded:: 3.2
 
+   .. versionchanged:: 3.3
+      Added the optional *prefixes* parameter.
+
 
 .. function:: getuserbase()