Prevent user trying to run dirs on "/"

dirs

@@ -35,6 +35,10 @@ unless (-d $dir_path) {
     die "$dir_path is not a directory\n"
 }
 
+if ($dir_path eq '/') {
+    die "You are not able to run 'dirs' on the root directory\n"
+}
+
 my $total_size = 0;
 
 sub calculate_size {