Add a few extra hints in the Scintilla update script

scripts/update-scintilla.sh

@@ -70,7 +70,10 @@ if git status -unormal -s scintilla | grep '^??'; then
 Untracked files above have been introduced by the new Scintilla version and
 should be added to version control if appropriate, or removed.
 
-Don't forget to add new files to the build system.
+You can add them to Git with the command:
+$ git add $(git status -unormal -s scintilla | grep '^??' | cut -b4- | sed '$!{s/$/ \\/};1!{s/^/          /}')
+
+Don't forget to add new files to the build system (scintilla/Makefile.am).
 EOF
 fi