Fix site module docstring to match the code

Lib/site.py

@@ -13,8 +13,8 @@ works).
 This will append site-specific paths to the module search path.  On
 Unix, it starts with sys.prefix and sys.exec_prefix (if different) and
 appends lib/python<version>/site-packages as well as lib/site-python.
-On other platforms (mainly Mac and Windows), it uses just sys.prefix
-(and sys.exec_prefix, if different, but this is unlikely).  The
+On other platforms (mainly Mac and Windows), it tries each of the
+prefixes directly, as well as with lib/site-packages appended.  The
 resulting directories, if they exist, are appended to sys.path, and
 also inspected for path configuration files.