Merge pull request #165 from arduino/aentinger-patch-2

Fix: Providing documentation for various cores how to manually integrate ArduinoCore-API.

Author: facchinm

Diff for: README.md

@@ -77,6 +77,11 @@ In order to compile a core which is implementing ArduinoCore-API you'll need to
 tar --exclude='*.git*' -cjhvf $yourcore-$version.tar.bz2 $yourcore/
 ```
 
+Documentation for how to integrate with a Arduino core (which is necessary if you do not download the Arduino core via the Boards Manager) can be found here:
+* [ArduinoCore-megaavr](https://github.com/arduino/ArduinoCore-megaavr#developing)
+* [ArduinoCore-mbed](https://github.com/arduino/ArduinoCore-mbed#clone-the-repository-in-sketchbookhardwarearduino-git)
+* [ArduinoCore-samd](https://github.com/arduino/ArduinoCore-samd/#developing)
+
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