update README to clarify how to generate the current draft]

----- Forwarded message from Christoph Hellwig <hch@infradead.org> -----

Date: Mon, 4 Nov 2013 11:04:51 -0800
From: Christoph Hellwig <hch@infradead.org>
Subject: [PATCH] update README to clarify how to generate the current draft
To: nfsv4@ietf.org

Document how to generate the current draft, otherwise dumb people like
me expect the actually checked in older drafts to be the most recent
ones available in the repository.