Adds readme for block editor component tool-selector

[AkmElias]

What?

Adds missing readme for block editor component tool-selector

Why?

The tool-selector component was missing the necessary readme.

How?

This PR is addressing the issue #22891

Testing Instructions

Testing Instructions for Keyboard

Screenshots or screencast

[github-actions]

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Co-authored-by: AkmElias <akmelias@git.wordpress.org>

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[github-actions]

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