Stylus gentle intro overhaul

[anegg0]

This PR aims at improving Stylus' gentle intro by:

• Adding a use case section
• Improving the text's readability, syntax and grammar
• Updating deprecated refs, e.g., Stylus is now on Sepolia
• Adding quicklooks
• Adding links to useful resources

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Name	Status	Preview	Updated (UTC)
arbitrum-docs	✅ Ready (Inspect)	Visit Preview	Sep 3, 2024 7:19pm