doc: update DCO to v1.1

PR-URL: #5170
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Myles Borins <myles.borins@gmail.com>

CONTRIBUTING.md

@@ -173,19 +173,28 @@ to address, apply your changes in a separate commit and push that to your
 feature branch. Post a comment in the pull request afterwards; GitHub does
 not send out notifications when you add commits.
 
-
-## Developer's Certificate of Origin 1.0
+## 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
+  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
+  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.
+  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.