Improve vignette

[Jason Vander Heiden]

The cloning vignette doesn’t read like a tutorial or walkthrough. Most of it is a repeat of the man pages and I think that’s distracting. Thoughts:

1. Doesn't state the purpose at the beginning (we want clones, here's how we get clones).
2. Has a "Functions" section rather than being broken down by clonal clustering methodology.
3. Has big chunks explaining the function arguments, which repeats the man pages and doesn't walk you through actually using the package.

Shorter is better, in my opinion. Just focus on what's important to get people started with the package and leave the advanced details to the man pages.

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[ssnn]

I am changing ‘assignee’ to Nima, because he took over.

[nima nouri]

finalized by 26acf7a