radio-puzzle: add some explanation about

beginner/apps/src/bin/radio-puzzle-1.rs

@@ -17,6 +17,7 @@ fn main() -> ! {
     // puzzle.hex uses channel 25
     radio.set_channel(Channel::_25);
 
+    // the IEEE 802.15.4 packet that will carry our data
     let mut packet = Packet::new();
 
     // first exchange a single packet with the Dongle

beginner/apps/src/bin/radio-puzzle-solution-2.rs

@@ -23,6 +23,7 @@ fn main() -> ! {
     /* # Build a dictionary */
     let mut dict = LinearMap::<u8, u8, consts::U128>::new();
 
+    // the IEEE 802.15.4 packet that will carry our data
     let mut packet = Packet::new();
     for plainletter in 0..=127 {
         packet.copy_from_slice(&[plainletter]);

beginner/apps/src/bin/radio-puzzle-solution.rs

@@ -24,6 +24,7 @@ fn main() -> ! {
     let mut dict = LinearMap::<u8, u8, consts::U128>::new();
     //                                 ^^^^^^^^^^^^ NOTE larger capacity
 
+    // the IEEE 802.15.4 packet that will carry our data
     let mut packet = Packet::new();
     for plainletter in 0..=127 {
         //             ^^^^^^^ NOTE complete ASCII range