Add "How to use AWS CLI" section to Readme

[nelsonic]

Can we simplify our examples by encouraging people to use the CLI early in the process...?
https://aws.amazon.com/cli/

[jackcarlisle]

@nelsonic how early do you think? I was thinking we could give an introduction to the CLI after the basic examples section which would mean that we could simplify ALOT of our subsequent examples

[nelsonic]

Agreed. 👍
The end-to-end example that I'm (still) working on is all Screenshots... but I've realised that it would be much faster with CLI... I might write a "Part 2" that uses CLI instead.