Add code of conduct. (#430)

* Add code of conduct.
* Move into .github folder.

.github/CODE_OF_CONDUCT.md

@@ -0,0 +1,5 @@
+## Code of Conduct
+This project has adopted the [Amazon Open Source Code of Conduct](https://aws.github.io/code-of-conduct).
+For more information see the [Code of Conduct FAQ](https://aws.github.io/code-of-conduct-faq) or contact
+opensource-codeofconduct@amazon.com with any additional questions or comments.
+