Merge pull request #94 from 0xc0170/fix_license

add contributing file

Author: Seppo Takalo

CONTRIBUTING.md

@@ -0,0 +1,5 @@
+# Contributing to Mbed OS
+
+Mbed OS is an open-source, device software platform for the Internet of Things. Contributions are an important part of the platform, and our goal is to make it as simple as possible to become a contributor.
+
+To encourage productive collaboration, as well as robust, consistent and maintainable code, we have a set of guidelines for [contributing to Mbed OS](https://os.mbed.com/docs/mbed-os/latest/contributing/index.html).

README.md

@@ -451,3 +451,9 @@ Serial pc(TX, RX);
 pc.printf("...");    // Replace printf with pc.printf in the example
 ```
 
+### License and contributions
+
+The software is provided under Apache-2.0 license. Contributions to this project are accepted under the same license. Please see [contributing.md](CONTRIBUTING.md) for more info.
+
+This project contains code from other projects. The original license text is included in those source files. They must comply with our license guide.
+