docs: streamline README for first-time visitors

[Copilot]

The README was overly long and hindered first-visit comprehension.

• Overview: Trimmed to core value props (L7 whitelisting, host enforcement, Docker-in-Docker).
• Quick start: Minimal install/run snippet with a one-line Copilot example; added note to review or manually verify the installer.
• Navigation: Pointed to existing detailed docs (usage, logging quick ref, squid log filtering, security, architecture, troubleshooting).
• Development: Kept only essential npm commands.

Example quick start:

curl -sSL https://raw.githubusercontent.com/githubnext/gh-aw-firewall/main/install.sh | sudo bash
sudo awf --allow-domains github.com -- curl https://api.github.com

Original prompt

README is getting bloated. please shorten it so that it provides a place for first visiter to understand this project without displaying too much information at once.

Custom agent used: technical-doc-writer
AI technical documentation writer for awf library using Astro Starlight

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