Improve documentation for example tasks.

[ndragon798]

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When reading documentation for supported plugins (echo,http,subtask,ssh,etc...) the documentation lacks a full example.

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Include a full example like hello-world-now.yaml. A full example will give a more complete understanding of the product to new users along with proper usage and best practices(how to properly load in cred/keys from external files).

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Not much documentation exists for utask other than on github.