Update CONTRIBUTING via new community contribution flow

CONTRIBUTING.md

@@ -21,6 +21,7 @@ _This notice should stay as the first item in the CONTRIBUTING.md file._
 <!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
 **Table of Contents**  *generated with [DocToc](https://github.com/thlorenz/doctoc)*
 
+- [Developer Certificate of Origin + License](#developer-certificate-of-origin--license)
 - [Contributing Documentation has been moved](#contributing-documentation-has-been-moved)
 - [Contribute to GitLab](#contribute-to-gitlab)
 - [Security vulnerability disclosure](#security-vulnerability-disclosure)
@@ -36,7 +37,7 @@ _This notice should stay as the first item in the CONTRIBUTING.md file._
   - [Release Scoping labels](#release-scoping-labels)
   - [Priority labels](#priority-labels)
   - [Severity labels](#severity-labels)
-     - [Severity impact guidance](#severity-impact-guidance)
+    - [Severity impact guidance](#severity-impact-guidance)
   - [Label for community contributors](#label-for-community-contributors)
 - [Implement design & UI elements](#implement-design--ui-elements)
 - [Issue tracker](#issue-tracker)
@@ -70,7 +71,7 @@ to contribute to GitLab in a way that is easy for everyone.
 For a first-time step-by-step guide to the contribution process, please see
 ["Contributing to GitLab"](https://about.gitlab.com/contributing/).
 
-Looking for something to work on? Look for issues with the label [Accepting Merge Requests](#i-want-to-contribute).
+Looking for something to work on? Look for issues in the [Backlog (Accepting merge requests) milestone](#i-want-to-contribute).
 
 GitLab comes into two flavors, GitLab Community Edition (CE) our free and open
 source edition, and GitLab Enterprise Edition (EE) which is our commercial
@@ -151,8 +152,8 @@ the remaining issues on the GitHub issue tracker.
 
 ## I want to contribute!
 
-If you want to contribute to GitLab [issues with the label `Accepting Merge Requests` and small weight][accepting-mrs-weight]
-is a great place to start. Issues with a lower weight (1 or 2) are deemed
+If you want to contribute to GitLab, [issues in the  `Backlog (Accepting merge requests)` milestone with small weight][https://gitlab.com/gitlab-org/gitlab-ce/issues?scope=all&utf8=✓&state=opened&assignee_id=0&milestone_title=Backlog%20(Accepting%20merge%20requests)]
+are a great place to start. Issues with a lower weight (1 or 2) are deemed
 suitable for beginners. These issues will be of reasonable size and challenge,
 for anyone to start contributing to GitLab. If you have any questions or need help visit [Getting Help](https://about.gitlab.com/getting-help/#discussion) to
 learn how to communicate with GitLab. If you're looking for a Gitter or Slack channel