add some missing docs for PKCS8SerializationBackend, update changelog
diff --git a/docs/hazmat/backends/openssl.rst b/docs/hazmat/backends/openssl.rst
index 6ad0d04..e829798 100644
--- a/docs/hazmat/backends/openssl.rst
+++ b/docs/hazmat/backends/openssl.rst
@@ -19,7 +19,9 @@
* :class:`~cryptography.hazmat.backends.interfaces.HashBackend`
* :class:`~cryptography.hazmat.backends.interfaces.HMACBackend`
* :class:`~cryptography.hazmat.backends.interfaces.PBKDF2HMACBackend`
+ * :class:`~cryptography.hazmat.backends.interfaces.PKCS8SerializationBackend`
* :class:`~cryptography.hazmat.backends.interfaces.RSABackend`
+ * :class:`~cryptography.hazmat.backends.interfaces.TraditionalOpenSSLSerializationBackend`
It also exposes the following: