Add "Why" and "How" sections to README

[Copilot]

README lacked motivation and workflow explanation, making it hard for new users to understand the tool's value proposition and usage model.

Changes

• Added "Why Use This?" section - Identifies 4 pain points (scattered context, repetition, token limits, manual onboarding) and maps each to a solution
• Added "When to Use" section - Lists 5 concrete use cases (AI agents, team standardization, complex projects, onboarding, multi-environment)
• Added "How It Works" section - 4-step workflow with ASCII diagram showing memory/prompt composition pipeline
• Reorganized structure - Changed flow from Installation → Usage to Why → When → How → Installation → Usage
• Enhanced Quick Start - Converted numbered list to labeled steps with inline explanations and output example
• Fixed all examples - Added empty frontmatter (---\n---) to markdown files to work around parser bug that skips first line when checking for frontmatter

Example

Before (unclear what user gets):

# Task: {{ .taskName }}
Please help with this task.

After (explicit frontmatter preserves content):

---
---
# Task: {{ .taskName }}
Please help with this task.

Original prompt

I think we need a clear explaination of why you want to use this, and how to use it.

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