Add USE_CASES.md and use-case-images directory with example images

[sevfitz]

Closes #56

Checklist

• [x] I have made a material change to the repo (functionality, testing, spelling, grammar)
• [x] I have read the [Contribution Guide] and my PR follows them.
• [x] I updated my branch with the master branch.
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] 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:

• Creates USE_CASES.md with description of simple use case
• Creates use-cases-images/ containing three screenshot images

Thank you!

[mbernier]

@two24studios @ksigler7 This is amazing. Check it out!

Thank you @sevfitz!!

[thinkingserious]

Hello @sevfitz,

Thanks again for the PR!

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

Team SendGrid DX

[mbernier]

If you are interested, we would love the opportunity to talk to you about Hacktoberfest and our API libraries.

Our agenda would be: Explore what you liked and is there anything we can do to improve?

You can grab a time on my calendar that works for you and we can have a chat on Google Hangout or Skype. If you prefer, you can email me using my GitHub username at my company’s domain.

Thank you so much,

Matt Bernier - @mbernier - SendGrid Developer Experience Product Manager Elmer Thomas - @thinkingserious - SendGrid Developer Experience Engineer @SendGrid

[apigirl]

this is really neat! thanks for sharing! I've added this as one of our resources when we redo the templating doc soon.