Add DCO requirements and updated code of conduct (#235)

Issue reference: dapr/docs#2039

Signed-off-by: Will <[email protected]>

Author: willtsai

CONTRIBUTING.md

@@ -2,7 +2,13 @@
 
 Thank you for your interest in Dapr Go SDK!
 
-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.
+This project welcomes contributions and suggestions. Most contributions require you to signoff on your commits via 
+the Developer Certificate of Origin (DCO). When you submit a pull request, a DCO-bot will automatically determine 
+whether you need to provide signoff for your commit. Please follow the instructions provided by DCO-bot, as pull 
+requests cannot be merged until the author(s) have provided signoff to fulfill the DCO requirement.
+You may find more information on the DCO requirements [below](#developer-certificate-of-origin-signing-your-work).
+
+This project has adopted the [Contributor Covenant Code of Conduct](https://github.com/dapr/community/blob/master/CODE-OF-CONDUCT.md).
 
 Contributions come in many forms: submitting issues, writing code, participating in discussions and community calls.
 
@@ -59,6 +65,47 @@ All contributions come through pull requests. To submit a proposed change, we re
 
 A good way to communicate before investing too much time is to create a "Work-in-progress" PR and share it with your reviewers. The standard way of doing this is to add a "[WIP]" prefix in your PR's title and assign the **do-not-merge** label. This will let people looking at your PR know that it is not well baked yet.
 
+### Developer Certificate of Origin: Signing your work
+
+#### Every commit needs to be signed
+
+The Developer Certificate of Origin (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.
+
+```
+This is my commit message
+
+Signed-off-by: Random J Developer <[email protected]>
+```
+Git even has a `-s` command line option to append this automatically to your commit message:
+```
+$ git commit -s -m 'This is my commit message'
+```
+
+Each Pull Request is checked  whether or not commits in a Pull Request do contain a valid Signed-off-by line.
+
+#### I didn't sign my commit, now what?!
+
+No worries - You can easily replay your changes, sign them and force push them!
+
+```
+git checkout <branch-name>
+git commit --amend --no-edit --signoff
+git push --force-with-lease <remote-name> <branch-name>
+```
+
 ### Use of Third-party code
 
 - All third-party code must be placed in the `vendor/` folder.
@@ -74,4 +121,4 @@ A non-exclusive list of code that must be places in `vendor/`:
 
 ## Code of Conduct
 
-This project follows the [CNCF Code of Conduct](https://github.com/cncf/foundation/blob/master/code-of-conduct.md).
+This project has adopted the [Contributor Covenant Code of Conduct](https://github.com/dapr/community/blob/master/CODE-OF-CONDUCT.md)