LMGTFY:
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of the ArduinoGetStarted.com nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
Otherwise there are no clear restrictions on commercial re-sale - HOWEVER, since code is copyrighted (in the EU this happens automatically; in the US in principle as well, but registering copyright tends to help the author to assert their rights in any legal proceedings), it might be wise to check with the authors if commercial repackaging would also still fall under their conditions. If so, you should be safe provided you adhere to the limitations they laid down (which continue after the bit I quoted above).