Add TODO to README

README

@@ -7,8 +7,12 @@ We parse commands using a state machine so we can deal
 with small chunks of characters at a time and spit out
 the parsed command when the transmission has finished.
 
+TODO: System clock frequency should be a multiple of
+1.8432MHz for perfect USART. This means we would need
+an external crystal oscillator.
+
 TODO: Do we need to handle backspaces for interactive
-serial consoles?!
+serial consoles?! Overkill?!
 
 ### Supported Commands