Have the pem public/private key loading docs point to x.509
diff --git a/docs/hazmat/primitives/asymmetric/serialization.rst b/docs/hazmat/primitives/asymmetric/serialization.rst
index d5da24d..7ff4ce3 100644
--- a/docs/hazmat/primitives/asymmetric/serialization.rst
+++ b/docs/hazmat/primitives/asymmetric/serialization.rst
@@ -71,6 +71,14 @@
all begin with ``-----BEGIN {format}-----`` and end with ``-----END
{format}-----``.
+.. note::
+
+ A PEM block which starts with ``-----BEGIN CERTIFICATE-----`` is not a
+ public or private key, it's an :doc:`X.509 Certificate </x509>`. You can
+ load it using :func:`~cryptography.x509.load_pem_x509_certificate` and
+ extract the public key with
+ :meth:`Certificate.public_key <cryptography.x509.Certificate.public_key>`.
+
.. function:: load_pem_private_key(data, password, backend)
.. versionadded:: 0.6