Update README with concise sentences, update quickstart guide

[cdrage]

This updates the quickstart guide as well as the README.md and
introduction.md

I found that the points kind-of repeat themselves (See Concise and
Simplicity points).

Instead, alternative points such as "shortcuts" and reducing the overall
file-size of your file has been added.

Also, emphasizing that you can still use Kubernetes constructs within
your Kedge file.

[pradeepto]

I am not sure of the phrase "extensions". Because aren't CRDs extensions of Kubernetes?

[kadel]

Because aren't CRDs extensions of Kubernetes?

Don't think so.

But I agree that extension "An extensions of Kubebernetes" might not a bit misleading.

"An extensions of Kubebernetes definitions" or something along those lines, something that explains that is extending kubernetes artifacts/definitions

[cdrage]

@kadel @pradeepto Updated with your suggestions an extension of Kubernetes definitions