Bump to version 3.6.4, and add some notes about versions

setup.py

@@ -9,19 +9,29 @@
                      'to install the typing package.\n')
     exit(1)
 
-version = '3.6.2'
+version = '3.6.4'
 description = 'Type Hints for Python'
 long_description = '''\
 Typing -- Type Hints for Python
 
 This is a backport of the standard library typing module to Python
-versions older than 3.5.
+versions older than 3.5.  (See note below for newer versions.)
 
 Typing defines a standard notation for Python function and variable
 type annotations. The notation can be used for documenting code in a
 concise, standard format, and it has been designed to also be used by
 static and runtime type checkers, static analyzers, IDEs and other
 tools.
+
+NOTE: in Python 3.5 and later, the typing module lives in the stdlib,
+and installing this package has NO EFFECT.  To get a newer version of
+the typing module in Python 3.5 or later, you have to upgrade to a
+newer Python (bugfix) version.  For example, typing in Python 3.6.0 is
+missing the definition of 'Type' -- upgrading to 3.6.2 will fix this.
+
+Also note that most improvements to the typing module in Python 3.7
+will not be included in this package, since Python 3.7 has some
+built-in support that is not present in older versions (See PEP 560.)
 '''
 
 package_dir = {2: 'python2', 3: 'src'}[sys.version_info.major]