update boards doc

docs/boards.md

@@ -1,9 +1,9 @@
 # Boards
 
 The board support code is only used for self-contained examples and testing. It is not used when TinyUSB is part of a larger project. It is responsible for getting the MCU started and the USB peripheral clocked with minimal of on-board devices
-- One LED for status
-- One Button to get input from user
-- One UART optionally, mostly for host examples
+- One LED : for status
+- One Button : to get input from user
+- One UART : optional for device, but required for host examples
  
 ## Supported Boards