tool/run/grub2: user-friendly missing message

Ref #2526

tool/run/grub2.inc

@@ -7,11 +7,14 @@ proc get_grub2_dir { } {
 
 	if {![file exists $grub2_path]} {
 		puts ""
-		puts "GRUB2 binaries are missing."
-		puts "You can download the GRUB2 binaries by invoking:"
-		puts "\ttool/ports/prepare_port grub2"
+		puts "Port not prepared or outdated:"
+		puts "  grub2"
+		puts ""
+		puts "You can prepare respectively update it as follows:"
+		puts "  [genode_dir]/tool/ports/prepare_port grub2"
 		puts ""
 		exit 1
 	}
+
 	return $grub2_path
 }