Fix instructions for installing pickle with cgr

[jonphipps]

Description

cgr doesn't allow 'install' or 'global'.

I was also bit by the 'cgr alias' conflict in the oh-my-zsh project. But that's another issue.

Motivation and context

Why is this change required? What problem does it solve?

Couldn't install pickle with the supplied instructions. The instructions in the slides are wrong too.

How has this been tested?

Please describe in detail how you tested your changes.

Could install pickle! Yay.

Screenshots (if appropriate)

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

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