Update README.rst

pyca#5387

README.rst

@@ -21,7 +21,7 @@ pyca/cryptography
 
 ``cryptography`` is a package which provides cryptographic recipes and
 primitives to Python developers.  Our goal is for it to be your "cryptographic
-standard library". It supports Python 2.7, Python 3.5+, and PyPy 5.4+.
+standard library". It supports Python 2.7, Python 3.6+, and PyPy 5.4+.
 
 ``cryptography`` includes both high level recipes and low level interfaces to
 common cryptographic algorithms such as symmetric ciphers, message digests, and