added missing link (#15)

added missing link from https://www.arduino.cc/en/Reference/ArduinoRS485

Author: jhansson-ard

docs/readme.md

@@ -1,12 +1,12 @@
 # Arduino RS485 library
 
 
-The Arduino RS485 library enables you to send and receive data using the RS-485 standard with Arduino® RS485 Shields, like the MKR 485 Shield. Please refer to the MKR RS485 Shield documentation for the specific settings about half, full duplex, and termination.
+The Arduino RS485 library enables you to send and receive data using the RS-485 standard with Arduino® RS485 Shields, like the MKR 485 Shield. Please refer to the [MKR RS485 Shield](https://www.arduino.cc/en/Guide/MKR485Shield) documentation for the specific settings about half, full duplex, and termination.
 
 This library supports the MAX3157 and equivalent chipsets. 
 
 To use this library:
 
 ```
 #include <ArduinoRS485.h>
-```
+```