Update CONTRIBUTING - contribution guideline to branch off development

[myzeprog]

Fixes #106

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 tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

Short description of what this PR does:

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.

[codecov]

Codecov Report

Merging #107 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #107   +/-   ##
=======================================
  Coverage   91.34%   91.34%           
=======================================
  Files           6        6           
  Lines         289      289           
=======================================
  Hits          264      264           
  Misses         25       25

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[thinkingserious]

Hello @myzeprog,

Thanks again for the PR!

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Team SendGrid DX