Add "Merge Requests" section to the contributor's guide

Background

We need to add a section to our contributing.md guide to include what our minimum expectations before reviewing are and what we'll typically do through the merge request process.

Acceptance Criteria

• Notes are added to 'contributing.md' for:
  • minimum MR review requirements
  • POPs MR review process

Definition of Done

• An MR review section is added to the contributing.md guide
• The TOC for this guide is updated
• Consideration are made and details are added to the guide for outside contributor's MRs