Add purpose, license, legal disclaimer, and link to Code of Conduct

CONTRIBUTING.md

@@ -1 +1,14 @@
-We do not accept Pull Requests or other contributions to this repository. Feel free to comment or make suggestions, but note that we do not actively monitor contributions to this repository. If you would like to contact GitHub about this repository, please [contact support](https://github.com/contact).
+# Contributing
+
+Hi there! We're thrilled that you're interested in our Government Takedowns repo. As our [README](README.md) explains, 
+>the purpose of this repository is to publicly post notices that result in GitHub blocking content that a government notifies us is illegal. GitHub created this repository for transparency with our community when we block content in response to a complete government takedown notice. We publicly post those notices, unchanged (other than redactions of personal information), because we are concerned about Internet censorship, and believe that transparency on a specific and ongoing level is essential to good governance. 
+>
+>Discussion in this repo should relate to this purpose. 
+>
+>We do not accept Pull Requests in this repository because the notices we post are verbatim from the notifying government.
+
+Contributions to this project are dedicated to the public domain under [CC0-1.0](LICENSE.md).
+
+Remember that information in this repo [is not legal advice and comes without warranty](README.md#disclaimer).
+
+Please note that this project is released with a [Contributor Code of Conduct](CODE_OF_CONDUCT.md). By participating in this project you agree to abide by its terms.