docs(usart1 init): add comment to set the proper baud rate

Author: modulitos

src/11-usart/auxiliary/src/lib.rs

@@ -29,6 +29,9 @@ pub fn init() -> (&'static mut usart1::RegisterBlock, MonoTimer, ITM) {
     let rx = gpioa.pa10.into_af7(&mut gpioa.moder, &mut gpioa.afrh);
 
     Serial::usart1(dp.USART1, (tx, rx), 115_200.bps(), clocks, &mut rcc.apb2);
+    // If you are having trouble sending/receiving data to/from the
+    // HC-05 bluetooth module, try this configuration instead:
+    // Serial::usart1(dp.USART1, (tx, rx), 9600.bps(), clocks, &mut rcc.apb2);
 
     unsafe {
         (

src/13-serial-over-bluetooth/README.md

@@ -22,4 +22,6 @@ Recommended steps to wire this up:
 And that's it! You should be able to run all the programs you wrote in [section 11] without
 modification! Just make sure you open the right serial device / COM port.
 
+**NOTE** If you are having trouble communicating with the bluetooth device, you may need to initialize USART1 with a lower baud rate. Lowering it from 115,200 bps to 9,600 bps might help, as described [here](https://github.com/rust-embedded/discovery/blob/master/src/11-usart/auxiliary/src/lib.rs#L31)
+
 [section 11]: ../11-usart/index.html