Readme install instructions (#10)

* docs: add plain-english install instructions

Adds a brief line above the install commands so creatives who
haven't used a terminal before know what to do. Also removes the
leftover internal note about /setup-brain's naming.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* chore: remove plans/ folder from project

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: camawjones