Add DCO and updade CONTRIBUTING.md accordingly

CONTRIBUTING.md

@@ -1,7 +1,21 @@
-# Contributing to Jaeger
+# How to Contribute to Jaeger
 
-We'd love your help! If you would like to contribute code you can do so through GitHub
-by forking the repository and sending a pull request into the `master` branch.
+We'd love your help!
+
+Jaeger is [Apache 2.0 licensed](LICENSE) and accepts contributions via GitHub
+pull requests. This document outlines some of the conventions on development
+workflow, commit message formatting, contact points and other resources to make
+it easier to get your contribution accepted.
+
+We gratefully welcome improvements to documentation as well as to code.
+
+# Certificate of Origin
+
+By contributing to this project you agree to the [Developer Certificate of
+Origin](https://developercertificate.org/) (DCO). This document was created
+by the Linux Kernel community and is a simple statement that you, as a
+contributor, have the legal right to make the contribution. See the [DCO](DCO)
+file for details.
 
 ## Getting Started
 
@@ -82,7 +96,7 @@ issue](https://github.com/uber/jaeger/issues).* Discussing your proposed
 changes ahead of time will make the contribution process smooth for everyone.
 
 Once we've discussed your changes and you've got your code ready, make sure
-that tests are passing (`make test` or `make cover`) and open your PR! Your
+that tests are passing (`make test` or `make cover`) and open your PR. Your
 pull request is most likely to be accepted if it:
 
 * Includes tests for new functionality.

DCO

@@ -0,0 +1,37 @@
+Developer Certificate of Origin
+Version 1.1
+
+Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
+660 York Street, Suite 102,
+San Francisco, CA 94110 USA
+
+Everyone is permitted to copy and distribute verbatim copies of this
+license document, but changing it is not allowed.
+
+
+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.
+