Add Code Review Guide

Add Code Review Guide

This document highlights what reviewers such as maintainers and committers look
for when reviewing code. It sets expectations for code authors and provides
a framework for code reviewers.

Changes since v4
* Changed to comply with US English

Changes since v3
* Added example under *Workflow from a Reviewer's Perspective* section
* Fixed typos in text introduced in v2

Changes since v2 (introduced in v2)
* Extend introduction
* Add "Code Review Workflow" covering
  - "Workflow from a Reviewer's Perspective"
  - "Workflow from an Author's Perspective"
  - "Problematic Patch Reviews"
* Wrap to 80 characters
* Replace inline links with reference links to make
  wrapping easier

Signed-off-by: Lars Kurth <lars.kurth@citrix.com>
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