docs: Add code reviews to CONTRIBUTING.md

[dagjaneiro]

Closes #73

Checklist

• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the master branch.
• I have added necessary documentation about the functionality in the appropriate .md file

Short description of what this PR does:

• Adds code review contributing guidelines

[SendGridDX]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ dagjaneiro
❌ thinkingserious
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[thinkingserious]

@dagjaneiro

We have not been able to merge your Pull Request, but because you are awesome - we wanted to make sure you could still get a SendGrid Hacktoberfest shirt.

Please go fill out our swag form before Nov 5th and we will send the shirt! (We know that you might have tried this before and it didn’t work, sorry about that!)

You have till Nov 5th to fill out this form in order to get the Hacktoberfest shirt!

Thank you for contributing during Hacktoberfest! We hope to see you in the repos soon! Just so you know, we always give away a SendGrid shirt for your first ever non-Hacktoberfest PR that gets merged.

[jonjenkins]

LGTM

[jonjenkins]

LGTM

[thinkingserious]

Hello @dagjaneiro,

Thanks again for the PR!

We appreciate your contribution and look forward to continued collaboration. Thanks!

Team SendGrid DX