added proper header;

--- a/src/Pure/ProofGeneral/ROOT.ML	Fri Dec 29 18:46:02 2006 +0100
+++ b/src/Pure/ProofGeneral/ROOT.ML	Fri Dec 29 18:46:04 2006 +0100
@@ -1,3 +1,10 @@
+(*  Title:      Pure/ProofGeneral/ROOT.ML
+    ID:         $Id$
+    Author:     David Aspinall
+
+Proof General interface for Isabelle.
+*)
+
 use "pgip_types.ML";
 use "pgip_markup.ML";
 use "pgip_input.ML";