Add contribution information

Author: khadiwala

CONTRIBUTING.md

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+# Reporting bugs
+If you are a user and you find a bug, please submit an [issue](https://github.ibm.com/cs-team-atg/async-util/issues). Please try to provide sufficient information for someone else to reproduce the issue.
+
+# Pull requests
+Pull requests for features or bug fixes are welcome. If you are working on a large contribution, please file an issue first. Feel free to ask for help or ask questions about a possible contribution.
+
+## Individual Contributions
+This project uses the DCO for individual contributions. If you are contributing as an individual, simply include a "Signed-off-by" in the commit message (git commit -s) or in the pull request description. This indicates you agree the commit satisfies the [Developer Certificate of Origin](DCO1.1.txt).
+
+## Corporate Contributions
+If you are contributing to the project on behalf of a corporation (your company owns the IP you would like to contribute), then we must recieve a signed [CLA](cla.doc) for your company.

DCO1.1.txt

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+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.

README.md

@@ -117,3 +117,6 @@ CompletionStage<Result> makeRequest(Request request) {
 The package provides asynchronous versions of read/write locks, stamped locks, semaphores and named locks. The full [locks javadoc](https://pages.github.ibm.com/cs-team-atg/async-util/apidocs/com/ibm/async_util/locks/package-summary.html) contains more information.
 ## Util
 TODO
+
+## Contributing
+Contributions welcome! See [Contributing](CONTRIBUTING.md) for details.