Update 'README.md'

improve readme

README.md

@@ -2,17 +2,18 @@
 
 lets you use normal `printf()` in your code.
 
-## Adjustments to make
+### Adjustments to make
 the dafault configuration works on an atmega328p with 38400 baud. Any other setup might require one of the following changes.
 
-##### Set baudrate in 'uart.h'
+#### Set baudrate in 'uart.h'
 line 6:
 `#define BAUD 38400`
 
-##### Select which UART to use
+#### Select which UART to use
 If your controller has more than one UART hardware and you want to use a different than UART0,
 change the register defines in the following way:
 
+##### Example: UART0 -> UART3
 from `#define UART_BAUD_REGH UBRR0H` to `#define UART_BAUD_REGH UBRR3H`</br>
 and</br>
 from `#define UART_UCSZ0_BM UCSZ00` to `#define UART_UCSZ0_BM UCSZ30`