add license info

CONTRIBUTING.md

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+# How to contribute
+
+If you'd like to help us improve and extend BuckleScript, then we welcome your
+contributions!
+
+Below you will find some basic steps required to be able to contribute to the project. If
+you have any questions about this process or any other aspect of contributing to a Bloomberg open
+source project, feel free to send an email to [email protected] and we'll get your questions
+answered as quickly as we can.
+
+
+## Contribution Licensing
+
+Since BuckleScript is distributed under the terms of the [LGPL Version 3](LICENSE), contributions that you make
+are licensed under the same terms. In order for us to be able to accept your contributions,
+we will need explicit confirmation from you that you are able and willing to provide them under
+these terms, and the mechanism we use to do this is called a Developer's Certificate of Origin
+[DCO](DCO.md).  This is very similar to the process used by the Linux(R) kernel, Samba, and many
+other major open source projects.
+
+To participate under these terms, all that you must do is include a line like the following as the
+last line of the commit message for each commit in your contribution:
+
+    Signed-Off-By: Random J. Developer <[email protected]>
+
+You must use your real name (sorry, no pseudonyms, and no anonymous contributions).