Add Code Review section into Contributing.md

[omegamendes]

Fixes

Checklist

• [v] I have made a material change to the repo (functionality, testing, spelling, grammar)
• [v] I have read the [Contribution Guide] and my PR follows them.
• [v] I updated my branch with the master branch.
• [v] I have added tests that prove my fix is effective or that my feature works
• [v] I have added necessary documentation about the functionality in the appropriate .md file
• [v] I have added in line documentation to the code I modified

Short description of what this PR does:

-Add code review section into contributing.md file

If you have questions, please send an email to Sendgrid, or file a Github Issue in this repository.

[SendGridDX]

All committers have signed the CLA.

[childish-sambino]

Duplicate of #402