Update README.rst

Fix suggested by @diraol

Author: ramalho

18-asyncio-py3.7/README.rst

@@ -4,8 +4,8 @@ From the book "Fluent Python" by Luciano Ramalho (O'Reilly, 2015)
 http://shop.oreilly.com/product/0636920032519.do
 
 ##################################################################
-NOTE: this "18b" directory contains the examples of chapter 18
-rewritten using the new async/await syntax available in Python 3.5
-ONLY, instead of the "yield-from" syntax which works since Python
-3.3 (and will still work with Python 3.5).
+NOTE: this directory contains the examples of chapter 18
+rewritten using the new async/await syntax available from Python
+3.5+, instead of the "yield-from" syntax of Python 3.3 and 3.4.
+The code was tested with Python 3.7
 ##################################################################