add license to readme

Author: theScrabi

README.md

@@ -8,9 +8,19 @@ It can be used to create your own java based NewPipe client.
 A small example showing how to use the extractor can be found [here](https://github.com/TeamNewPipe/np-cli).
 
 ## Usage
-Using this Extractor in your own projects is simple. We offer this extractor as maven repository, so if you use
+Using this Extractor in your own open source projects is simple. We offer this extractor as maven repository, so if you use
 gradle you can simple include NewPipeExtractor to your project by adding this line to the dependencies:
 
 `compile 'com.github.TeamNewPipe:NewPipeExtractor:7ae274`
 
 A fill documentation is no yet there, but it will follow :) Stay tuned.
+
+
+## License
+[![GNU GPLv3 Image](https://www.gnu.org/graphics/gplv3-127x51.png)](http://www.gnu.org/licenses/gpl-3.0.en.html)  
+
+NewPipe is Free Software: You can use, study share and improve it at your
+will. Specifically you can redistribute and/or modify it under the terms of the
+[GNU General Public License](https://www.gnu.org/licenses/gpl.html) as
+published by the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.