Use runtime arguments to specify boot filename.

src/citra/citra.cpp

@@ -24,7 +24,7 @@ int __cdecl main(int argc, char **argv) {
 
 	System::Init(emu_window);
 
-    std::string boot_filename = "homebrew.elf";
+    std::string boot_filename = argv[1];
     std::string error_str;
     
     bool res = Loader::LoadFile(boot_filename, &error_str);