add CommonCrypto binding docs

docs/hazmat/bindings/commoncrypto.rst

@@ -0,0 +1,28 @@
+.. hazmat::
+
+CommonCrypto Binding
+====================
+
+.. currentmodule:: cryptography.hazmat.bindings.commoncrypto.binding
+
+These are `CFFI`_ bindings to the `CommonCrypto`_ C library. It is available on
+Mac OS X.
+
+.. class:: cryptography.hazmat.bindings.commoncrypto.binding.Binding()
+
+    This is the exposed API for the CommonCrypto bindings. It has two public
+    attributes:
+
+    .. attribute:: ffi
+
+        This is a :class:`cffi.FFI` instance. It can be used to allocate and
+        otherwise manipulate OpenSSL structures.
+
+    .. attribute:: lib
+
+        This is a ``cffi`` library. It can be used to call OpenSSL functions,
+        and access constants.
+
+
+.. _`CFFI`: https://cffi.readthedocs.org/
+.. _`CommonCrypto`: https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man3/Common%20Crypto.3cc.html#//apple_ref/doc/man/3cc/CommonCrypto

docs/hazmat/bindings/index.rst

@@ -20,3 +20,4 @@ Individual Bindings
     :maxdepth: 1
 
     openssl
+    commoncrypto