Update README.md

Author: mathiasbredholt

README.md

@@ -11,6 +11,7 @@ An Arduino library for using libmapper. Works with ESP32 Arduino only. Tested wi
 ```
 git clone --recursive https://github.com/mathiasbredholt/libmapper_arduino.git
 ```
+* Until the issue in https://github.com/mathiasbredholt/libmapper_arduino/issues/3 gets fixed the file in `~/Library/Arduino15/packages/esp32/hardware/esp32/1.0.4/tools/sdk/include/lwip/arpa/inet.h` needs to be updated as described in the issue.
 * Run
 ```
 make