Add license

[per1234]

The original author of this code is Paul Grayson. They published it as part of the pololu/libpololu-avr repository: https://github.com/pololu/libpololu-avr/blob/master/src/OrangutanResources/OrangutanResources.cpp

Although that file has a Creative Commons BY-SA 3.0 license, Paul Grayson has stated that the code may also be used under the MIT license of the pololu/libpololu-avr repository: https://github.com/maniacbug/MemoryFree/issues/5#issuecomment-414565532 https://github.com/pololu/libpololu-avr/blob/master/LICENSE.txt

Fixes https://github.com/maniacbug/MemoryFree/issues/5

CC: @Pharap

[landret]

Hi, is there a reason why this PR is still pending? That would be great if it could be accepted to confirm MIT license use. Thanks