Statement concerning appropriate use of I-D.

doc/drafts/README

+Internet-Drafts are working documents of the Internet Engineering Task
+Force (IETF), its areas, and its working groups.  Note that other groups
+may also distribute working documents as Internet-Drafts.
+
+Internet-Drafts are draft documents valid for a maximum of six months
+and may be updated, replaced, or obsoleted by other documents at any
+time.  It is inappropriate to use Internet-Drafts as reference material
+or to cite them other than as "work in progress."