Created a UseCases directory with a blank README to start.

[ed-parry]

Fixes #61

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:

• Adds a new Use Cases directory with a README file, which is linked from the main project README ready for use cases to be provided as and when they become available.

[SendGridDX]

All committers have signed the CLA.

[thinkingserious]

Hello @ed-parry,

Thanks again for the PR!

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Team SendGrid DX

[thinkingserious]

Hello @ed-parry,

Thanks again for the PR!

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Team SendGrid DX

[thinkingserious]

Hello @ed-parry,

Thanks again for the PR!

You have earned 1 out of the 5 points needed to receive glorious SendGrid Hacktoberfest swag.

Please take a moment to checkout this link to find more issues to get you past the required threshold or to simply continue the celebration.

Also, please be sure you have officially registered with us here by November 1, 2018 to qualify.

If you have any questions you can email us at [email protected].

Thank you and Happy Hacktobering!

Team SendGrid