Eliminate duplication between readmes

[t1m0thyj]

Currently there is a lot of overlap between the contents of the readme at the root of the repo (/README.md), and the readme for the Zowe CLI package (/packages/cli/README.md).

They have already fallen out of sync, with some changes made in just one file that should have been made in both.

I'm not sure exactly how the content should be split up, but believe we should update the readmes to contain distinct content geared to separate audiences. The readme at the root the repo has more visibility to CLI developers who find the CLI repository on GitHub, while the readme for the CLI package is shown to a wider audience on npmjs.com.

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