Add GitHub Pull Request template

Author: Martha Cryan

.github/PULL_REQUEST_TEMPLATE

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+
+
+ 
+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 Apache License 2.0; 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.
+