Prepare release 0.6.4

Change-Id: I5f72c2fbf2a2ec86c108a47b4c854b069267276b
diff --git a/docs/release-notes/release-notes-0.6.3.rst b/docs/release-notes/release-notes-0.6.3.rst
index 81c0e47..2b989cd 100644
--- a/docs/release-notes/release-notes-0.6.3.rst
+++ b/docs/release-notes/release-notes-0.6.3.rst
@@ -1,3 +1,5 @@
+.. _v0.6.3:
+
 NFD version 0.6.3
 -----------------