Add CONTRIBUTING.md contribution guidelines

CONTRIBUTING.md

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+Contributions to Nearenough are welcomed!
+
+## Process
+
+1. Fork the repo and create a feature branch for your work
+2. Commit your work on the branch
+3. Ensure all tests pass
+4. Open a Pull Request
+5. Discuss and iterate
+
+Notes
+* Keep pull requests limited to a single issue.
+* Keep whitespace-only commits separate from other code changes. If needed commit your new feature
+  or fix first then follow with a separate whitespace/style commit.
+
+## Testing
+
+* Any pull request that causes the test suite to fail will be rejected.
+* New features/functionality require new tests. 
+* Bugfixes should be accompanied by a test case covering the bug.
+* A pull request that reduces code coverage will likely be rejected.
+
+## Style/Coding Standard
+
+* Java 8 
+* Java code must comply with the
+  [Google Java Style Guide](https://google.github.io/styleguide/javaguide.html). This is strictly
+  enforced.
+* All files use unix (LF) line endings
+
+## External Dependencies
+
+Nearenough should be as unencumbered as possible. The `protocol` and `client` packages in particular
+strive to be bare-bones and may depend only on the Java 8 standard library, EdDSA-Java, and Netty.
+
+Contributions that introduce new external dependencies are very likely to be rejected.
+
+## Licensing of Contributions
+
+Section 5 of the Apache 2.0 license describes how contributions are handled:
+
+   > 5. Submission of Contributions. Unless You explicitly state otherwise,
+   >    any Contribution intentionally submitted for inclusion in the Work
+   >    by You to the Licensor shall be under the terms and conditions of
+   >    this License, without any additional terms or conditions.
+   >    Notwithstanding the above, nothing herein shall supersede or modify
+   >    the terms of any separate license agreement you may have executed
+   >    with Licensor regarding such Contributions.
+      
+### Contributor License Agreement
+
+One-liners, simple fixes, and other minor changes do **not** require a CLA. They are handled as per 
+Section 5 of the Apache 2.0 license. Prior to being merged into `master` you will be asked:
+
+  1. To confirm you are the original author of the work.
+  2. To state that you license the work to the Nearenough project under the Apache 2.0 license and 
+     that you have the legal authority to do so.
+
+Substantial contributions **do** require a completed Contributor License Agreement (CLA) prior to 
+them being accepted. The definition of "substantial" is fuzzy, but we'll know it when we see it. 
+Please contact stuart{at}int08h.com to get the CLA submitted.
+
+
+