Provide a little information about SDF, how to use it, and where to get it.h

doc/guide/README

+This module contains OpenLDAP guides in Simple Document Format (SDF).
+
+SDF is a freely available documentation system.  Based on a
+simple, readable markup language, SDF generates high quality
+output in multiple formats.
+
+    cd admin                # OpenLDAP Administrator's Guide
+    sdf -2topics index.sdf  # generate HTML for WWW publishing
+    sdf -2html guide.sdf    # generate HTML for release
+    sdf -2txt guide.sdf     # generate TXT for release
+
+More information (and SDF software) can be obtained from the
+SDF website at:
+    http://www.mincom.com/mtr/sdf/
+