Update contibuter docs to mention that DCO signoff is mandatory (#6)

Signed-off-by: Abhilash Shetty <[email protected]>

CONTRIBUTING.md

@@ -33,10 +33,14 @@ data-populator is an Apache 2.0 Licensed project and all your commits should be
     - DCO Signed
 * If your PR is not getting reviewed or you need a specific person to review it, please reach out to the OpenEBS Contributors. See [OpenEBS Community](https://github.com/openebs/openebs/tree/HEAD/community)
 
+---
+
 ## Sign your work
 
 We use the Developer Certificate of Origin (DCO) as an additional safeguard for the OpenEBS projects. This is a well established and widely used mechanism to assure that contributors have confirmed their right to license their contribution under the project's license. Please read [dcofile](https://github.com/openebs/openebs/blob/HEAD/contribute/developer-certificate-of-origin). If you can certify it, then just add a line to every git commit message:
 
+Please certify it by just adding a line to every git commit message. Any PR with Commits which does not have DCO Signoff will not be accepted:
+
 ````
   Signed-off-by: Random J Developer <[email protected]>
 ````
@@ -46,6 +50,7 @@ If you set your `user.name` and `user.email` in git config, you can sign your co
 
 You can also use git [aliases](https://git-scm.com/book/tr/v2/Git-Basics-Git-Aliases) like `git config --global alias.ci 'commit -s'`. Now you can commit with `git ci` and the commit will be signed.
 
+---
 ## Setting up your Development Environment
 
 This project is implemented using Go and uses the standard golang tools for development and build. In addition, this project heavily relies on Docker and Kubernetes. It is expected that the contributors: