tuned messages (again, see d50c2129e73a): presentation setup could fail initially for take some time;

--- a/src/Pure/Tools/build.scala	Fri Aug 19 20:07:41 2022 +0200
+++ b/src/Pure/Tools/build.scala	Fri Aug 19 20:11:15 2022 +0200
@@ -487,6 +487,7 @@
     if (!no_build && !progress.stopped && results.ok) {
       if (presentation_sessions.nonEmpty) {
         val presentation_dir = presentation.dir(store)
+        progress.echo("Presentation in " + presentation_dir.absolute)
         Presentation.update_root(presentation_dir)
 
         for ((chapter, infos) <- presentation_sessions.groupBy(_.chapter).iterator) {