Tagcopyrights, add contributing / licensing information

CONTRIBUTING.md

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+# How to contribute
+
+We'd love to accept your patches and contributions to this project. There are
+a just a few small guidelines you need to follow.
+
+## Contributor License Agreement
+
+Contributions to any Google project must be accompanied by a Contributor
+License Agreement. This is not a copyright **assignment**, it simply gives
+Google permission to use and redistribute your contributions as part of the
+project.
+
+If you are an individual writing original source code and you're sure you own
+the intellectual property, then you'll need to sign an [individual
+CLA](https://cla.developers.google.com/about/google-individual).
+
+If you work for a company that wants to allow you to contribute your work, then
+you'll need to sign a [corporate
+CLA](https://cla.developers.google.com/about/google-corporate).
+
+You generally only need to submit a CLA once, so if you've already submitted
+one (even if it was for a different project), you probably don't need to do it
+again.
+
+## Submitting a patch
+
+1.  It's generally best to start by opening a new issue describing the bug or
+    feature you're intending to fix. Even if you think it's relatively minor,
+    it's helpful to know what people are working on. Mention in the initial
+    issue that you are planning to work on that bug or feature so that it can
+    be assigned to you.
+
+1.  Follow the normal process of [forking](https://help.github.com/articles/fork-a-repo)
+    the project, and setup a new branch to work in. It's important that each
+    group of changes be done in separate branches in order to ensure that a
+    pull request only includes the commits related to that bug or feature.
+
+1.  Any significant changes should almost always be accompanied by tests. The
+    project already has good test coverage, so look at some of the existing
+    tests if you're unsure how to go about it.
+
+1.  All contributions must be licensed Apache 2.0 and all files must have a
+    copy of the boilerplate licence comment which can be generated by the
+    [autogen](https://github.com/mbrukman/autogen) tool.
+
+1.  Do your best to have [well-formed commit messages](http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html)
+    for each change. This provides consistency throughout the project, and
+    ensures that commit messages are able to be formatted properly by various
+    git tools.
+
+1.  Finally, push the commits to your fork and submit a [pull request](https://help.github.com/articles/creating-a-pull-request).