Message when no file args

src/main.cpp

@@ -50,11 +50,11 @@ int main(int argc, char* argv[]) {
             }
         }
         if (optind == argc) {
-            // here when no file args
+            print_help();
+            return EXIT_FAILURE;
         }
         for (int i = optind; i < argc; ++i) {
             try {
-                // process file argv[i]
                 write_image(std::cout, argv[i]);
             } catch (const std::runtime_error& ex) {
                 std::cerr << "termage: " << ex.what() << '\n';