add kernel panicking

src/main.rs

@@ -5,7 +5,8 @@ mod vga_buffer;
 
 use core::panic::PanicInfo;
 #[panic_handler]
-fn panic(_info: &PanicInfo) -> ! {
+fn panic(info: &PanicInfo) -> ! {
+    println!("{}", info);
     loop {}
 }
 
@@ -13,7 +14,7 @@ fn panic(_info: &PanicInfo) -> ! {
 #[no_mangle]
 pub extern "C" fn _start() -> ! {
     println!("Hello World!");
-
+    panic!("Nothing to do.");
 
     loop {}
 }