🚀 Feedback: Add a few use cases and diagrams in chapter 1

Improve the initial Docker description by adding some use cases and diagrams as per the feedback received [here](https://dev.to/billraymond/comment/1j907):

> Some feedback as someone completely new to Docker is that the definitions are good. However, you jump right into creating things and I would have preferred a few use cases and a few diagrams. I will go through your tutorials and they look easy enough.