Add some comments to the template's main.rs

template/src/main.rs

@@ -1,9 +1,24 @@
+// Games made using `agb` are no_std which means you don't have access to the standard
+// rust library. This is because the game boy advance doesn't really have an operating
+// system, so most of the content of the standard library doesn't apply.
+//
+// Provided you haven't disabled it, agb does provide an allocator, so it is possible
+// to use both the `core` and the `alloc` built in crates.
 #![no_std]
+// `agb` defines its own `main` function, so you must declare your game's main function
+// using the #[agb::entry] proc macro. Failing to do so will cause failure in linking
+// which won't be a particularly clear error message.
 #![no_main]
 
+// This is required in order to ensure that the panic handler defined in `agb` is set
+// up correctly.
 extern crate agb;
+
 use agb::{display, syscall};
 
+// The main function must take 0 arguments and never return. The agb::entry decorator
+// ensures that everything is in order. `agb` will call this after setting up the stack
+// and interrupt handlers correctly.
 #[agb::entry]
 fn main() -> ! {
     let mut gba = agb::Gba::new();