docs: replace CLA requirement with DCO

Signed-off-by: Simon Leet <simon.leet@microsoft.com>

CONTRIBUTING.md

@@ -1,6 +1,6 @@
 # Contributing to the Project
 
-Welcome! We are very happy to accept community contributions to the project, whether through [filing issues](#contributing-issues) or [code](#contributing-code) in the form of [Pull Requests](#pull-requests). Please note that by participating in this project, you agree to abide by the [Code of Conduct](./CODE_OF_CONDUCT.md), as well as the terms of the [Contributor License Agreement](#contributor-license-agreement-cla).
+Welcome! We are very happy to accept community contributions to the project, whether through [filing issues](#contributing-issues) or [code](#contributing-code) in the form of [Pull Requests](#pull-requests). Please note that by participating in this project, you agree to abide by the [Code of Conduct](./CODE_OF_CONDUCT.md), as well as the terms of the [Developer Certificate of Origin](#developer-certificate-of-origin-dco).
 
 ## Contributing Issues
 
@@ -65,15 +65,61 @@ We suggest:
 * Use a [concise, imperative description](https://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html) of the changes included in the `<short summary>` of the header, the body of the PR, and generally in your commit messages.
 * Use [GitHub keywords](https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/using-keywords-in-issues-and-pull-requests) in the footer of your PR description, such as `closes` to automatically close issues the PR intends to address.
 
-## Contributor License Agreement (CLA)
-
-This project welcomes contributions and suggestions.  Most contributions require you to agree to a
-Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us
-the rights to use your contribution. For details, visit https://cla.opensource.microsoft.com.
-
-When you submit a pull request, a CLA bot will automatically determine whether you need to provide
-a CLA and decorate the PR appropriately (e.g., status check, comment). Simply follow the instructions
-provided by the bot. You will only need to do this once across all repos using our CLA.
+## Developer Certificate of Origin (DCO)
+
+The [Developer Certificate of Origin](https://wiki.linuxfoundation.org/dco) (DCO) is a lightweight way for contributors to certify that they wrote or otherwise have the right to submit the code they are contributing to the project. Here is the [full text of the DCO](https://developercertificate.org/), reformatted for readability:
+
+> 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.
+
+Contributors _sign-off_ that they adhere to these requirements by adding a `Signed-off-by` line to commit messages.
+
+```text
+This is my commit message
+
+Signed-off-by: Random J Developer <random@developer.example.org>
+```
+
+Git even has a `-s` command line option to append this automatically to your commit message:
+
+```bash
+git commit -s -m 'This is my commit message'
+```
+
+Pull requests that do not contain a valid `Signed-off-by` line cannot be merged.
+
+### I didn't sign my commit, now what?
+
+No worries - You can easily amend your commit with a sign-off and force push the change to your submitting branch:
+
+```bash
+git switch <branch-name>
+git commit --amend --no-edit --signoff
+git push --force-with-lease <remote-name> <branch-name>
+```
+
+## Code of Conduct
 
 This project has adopted the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/).
 For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or