Update Intro section and add concepts

[srinjoyc]

This PR aims to refresh the content on the gentle introduction page by separating out conceptual information to a new concepts section. While the themes of the content and general structure was preserved, several edits are made to improve readability, update key items based on new information, and align better with the developer journey.

Updates:

• In a nutshell section revised to 3 points reflective of top value props of stylus
• Use cases are more detailed and aligned to value props, with a focus on efficient on-chain verification, DeFi instruments, and high-performance on-chain logic (reflects what most builders are using Stylus for and would be effective in doing so), linking to a specific case study.
• Offers a step-by-step guide on getting started with direct links to resources like the quickstart, examples, tutorials, and community channels (Telegram, Discord, GitHub). Note: Some of these will need to be updated before merging to master (relies on other content section like tutorials existing).
• Contains more hyperlinks to resources
• Actively seeks developers for building and contributing, emphasizing the $5M grant funding through the Stylus Sprint.
• Updates some language

Removes

• Public Preview banner from the gentle introduction page
• Conceptual content on 'how Stylus works' to a new page

[cla-bot]

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[vercel]

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Name	Status	Preview	Updated (UTC)
arbitrum-docs	✅ Ready (Inspect)	Visit Preview	Nov 6, 2024 6:30pm

[cla-bot]

Thank you for your pull request and welcome to our community. We could not parse the GitHub identity of the following contributors: srinjoyc.
This is most likely caused by a git client misconfiguration; please make sure to:

1. check if your git client is configured with an email to sign commits git config --list | grep email
2. If not, set it up using git config --global user.email email@example.com
3. Make sure that the git commit email is configured in your GitHub account settings, see https://github.com/settings/emails

[hkalodner]

Absolutely links like this need to be like https://t.me/arbitrum_stylus

[hkalodner]

That's why the vercel preview failed

[srinjoyc]

ty! fixed

[anegg0]

This overhaul helps put the right info in front of the right users, I think it's a great job.
I added a few nits, but LGTM