Create CONTRIBUTING.md

Added new file: CONTRIBUTING.md

Author: padamstx

CONTRIBUTING.md

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+# Issues
+
+If you encounter an issue with the project, you are welcome to submit a [bug report](https://github.com/IBM/java-sdk-core/issues).
+Before that, please search for similar issues. It's possible that someone has already reported the problem.
+
+# Pull Requests
+
+If you want to contribute to the repository, here's a quick guide:
+  1. Fork the repository
+  2. Develop and test your code changes:
+      * To build/test: `mvn clean package`
+      * Please add one or more tests to validate your changes.
+  3. Make sure everything builds/tests cleanly
+  4. Commit your changes  
+  5. Push to your fork and submit a pull request to the **master** branch
+
+# Developer's Certificate of Origin 1.1
+
+By making a contribution to this project, I certify that:
+
+(a) The contribution was created in whole or in part by me and I
+   have the right to submit it under the open source license
+   indicated in the file; or
+
+(b) The contribution is based upon previous work that, to the best
+   of my knowledge, is covered under an appropriate open source
+   license and I have the right under that license to submit that
+   work with modifications, whether created in whole or in part
+   by me, under the same open source license (unless I am
+   permitted to submit under a different license), as indicated
+   in the file; or
+
+(c) The contribution was provided directly to me by some other
+   person who certified (a), (b) or (c) and I have not modified
+   it.
+
+(d) I understand and agree that this project and the contribution
+   are public and that a record of the contribution (including all
+   personal information I submit with it, including my sign-off) is
+   maintained indefinitely and may be redistributed consistent with
+   this project or the open source license(s) involved.
+
+## Additional Resources
++ [General GitHub documentation](https://help.github.com/)
++ [GitHub pull request documentation](https://help.github.com/send-pull-requests/)
+
+[Maven]: https://maven.apache.org/guides/getting-started/maven-in-five-minutes.html