Update oh-my-zsh steps to make it easier for installation, and to use custom folder

[natecorkish]

Currently the steps don't show how to install the plugin to a custom oh-my-zsh installation folder

Type of changes

Changed from cd to the folder to cloning directly in to the custom/default folder.

• A helper script
• A link to an external resource like a blog post or video
• Text cleanups/updates

Checklist:

• All new and existing tests pass.
• Any scripts added use #!/usr/bin/env interpreter instead of potentially platform-specific direct paths (#!/bin/sh is an ok exception)
• Scripts are marked executable
• Scripts do not have a language file extension unless they are meant to be sourced and not run standalone. No one should have to know if a script was written in bash, python, ruby or whatever. Not including file extensions makes it easier to rewrite the script in another language later without having to change every reference to the previous version.
• I have added a credit line to README.md for the script
• If there was no author credit in a script added in this PR, I have added one.
• I have confirmed that the link(s) in my PR are valid.
• I have read the CONTRIBUTING document.

License Acceptance

• This repository is Apache version 2.0 licensed (some scripts may have alternate licensing inline in their code) and by making this PR, I am contributing my changes to the repository under the terms of the Apache 2 license.

[qlty-cloud-legacy]

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[unixorn]

LGTM. Not sure how I missed seeing this PR for so long, sorry. Thanks for the contribution, I use zgenom myself so the oh-my-zsh instructions were stale.