Update README.md

README.md

@@ -69,7 +69,7 @@ Watch this repo for new updates! And of course, contributions are welcome ;)
 
 When using ```SoftwareSerial``` (on Uno, Nano, etc), the speed **115200** may not work.  
 Try selecting **57600**, **38400**, or even lower - the one that works best for you.  
-Be sure to set correct TX/RX pins in the sketch.  
+Be sure to set correct TX/RX pins in the sketch. Please note that not every Arduino pin can serve as TX or RX pin.  
 **Read more about SoftSerial options and configuration [here](https://www.pjrc.com/teensy/td_libs_AltSoftSerial.html).**
 
 ### Diagnostics sketch