added docs for get_extension_for_class
diff --git a/docs/x509/reference.rst b/docs/x509/reference.rst
index 8d5d6a6..efc2c8a 100644
--- a/docs/x509/reference.rst
+++ b/docs/x509/reference.rst
@@ -889,6 +889,21 @@
>>> cert.extensions.get_extension_for_oid(ExtensionOID.BASIC_CONSTRAINTS)
<Extension(oid=<ObjectIdentifier(oid=2.5.29.19, name=basicConstraints)>, critical=True, value=<BasicConstraints(ca=True, path_length=None)>)>
+ .. method:: get_extension_for_class(extclass)
+
+ :param extclass: An extension class.
+
+ :returns: An instance of the extension class.
+
+ :raises cryptography.x509.ExtensionNotFound: If the certificate does
+ not have the extension requested.
+
+ .. doctest::
+
+ >>> from cryptography import x509
+ >>> cert.extensions.get_extension_for_class(x509.BasicConstraints)
+ <Extension(oid=<ObjectIdentifier(oid=2.5.29.19, name=basicConstraints)>, critical=True, value=<BasicConstraints(ca=True, path_length=None)>)>
+
.. class:: Extension
.. versionadded:: 0.9