Added basic download input logic

src/main.cpp

@@ -3,15 +3,27 @@
 #include <iostream>
 #include <string>
 int main(int argc, char **argv) {
+
   CLI::App app{"Spotify Downloader"};
 
-  std::string url;
+  app.require_subcommand(1);
 
-  app.add_option("-u,--url", url, "Spotify item URL");
+  auto *cmd_download =
+      app.add_subcommand("download", "Download tracks directly");
+  auto *cmd_convert =
+      app.add_subcommand("convert", "Convert assets between platforms");
+
+  std::string url;
+  cmd_download->add_option("url", url, "Target URL for Playlist or Song")
+      ->required();
+
+  std::string output;
+  cmd_download->add_option("output", output, "Output filename or directory")
+      ->required(false);
 
   CLI11_PARSE(app, argc, argv);
 
-  if (!url.empty()) {
+  if (cmd_download->parsed()) {
     std::cout << "Target URL: " << url << "\n";
   }