Deprecate Python 3.3 support, with the intention of being removed in the next release (#3566)

* Deprecate Python 3.3 support, with the intention of being removed in the next release

* whoops
diff --git a/docs/installation.rst b/docs/installation.rst
index 9ee966a..8acac2e 100644
--- a/docs/installation.rst
+++ b/docs/installation.rst
@@ -24,6 +24,8 @@
     Python 2.6 is no longer supported by the Python core team. A future version
     of cryptography will drop support for this version.
 
+    Python 3.3 support will be removed in the next cryptography release.
+
 We test compiling with ``clang`` as well as ``gcc`` and use the following
 OpenSSL releases: