add HKDF to changelog
diff --git a/docs/changelog.rst b/docs/changelog.rst
index f401fe7..2de9a32 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -15,6 +15,7 @@
 * Fixed compilation on systems where OpenSSL's ``ec.h`` header is not
   available, such as CentOS.
 * Added :class:`~cryptography.hazmat.primitives.kdf.pbkdf2.PBKDF2HMAC`.
+* Added :class:`~cryptography.hazmat.primitives.kdf.hkdf.HKDF`.
 
 0.1 - 2014-01-08
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