CONTRIBUTING.md: add instructions to sign commits

Signed-off-by: Vallari Agrawal <[email protected]>

CONTRIBUTING.md

@@ -137,7 +137,64 @@ conda activate teuthology-api
 
 3. Add yourself to the list of contributors in `AUTHORS.rst`.
 
-4. When you’re done editing, do:
+### Sign your work
+
+The sign-off is a simple line at the end of the explanation for the
+commit, which certifies that you wrote it or otherwise have the right to
+pass it on as a open-source patch. The rules are pretty simple: if you
+can certify the below:
+
+> **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.
+
+then you just add a line saying:
+
+```
+Signed-off-by: Random J Developer <[email protected]>
+```
+
+using your real name (sorry, no pseudonyms or anonymous contributions).
+
+**Git can sign off on your behalf**
+
+Please note that git makes it trivially easy to sign commits. First, set the
+following config options:
+
+    $ git config --list | grep user
+    [email protected]
+    user.name=My Real Name
+
+Then just remember to use ``git commit -s``. Git will add the ``Signed-off-by``
+line automatically.
+
+Additionally, commits needs to be GPG signed. Instructions to sign your commits can be found [here](https://docs.github.com/en/authentication/managing-commit-signature-verification/signing-commits). This will result in your commits showing up with a "Verified" badge on Github - read [here](https://docs.github.com/en/authentication/managing-commit-signature-verification/about-commit-signature-verification) for more details.
+
+### Commiting your changes
+
+1. When you’re done editing your changes, do:
 
    ```
    git add <MODIFIED FILES>
@@ -165,7 +222,7 @@ conda activate teuthology-api
    to look for recurring communication patterns.
    :::
 
-5. Please check that your changes don't break any unit tests with:
+2. Please check that your changes don't break any unit tests with:
 
    ```
    tox