docs: fix invalid link, modify texts

[osrm]

Introduction 📟

• Fix invalid link and modify texts

Purpose ℹ️

• Reflect that XMTP Community Forums is the main discussion channel and improve wording consistency.

Scope 🔭

• Replaced the "Q&A discussions" link with the "XMTP Community Forums" link and label
• Updated bug report and feature request wording for clarity and consistency with other docs.
• This PR was updated with reference to https://github.com/xmtp/xmtp-js/blob/main/CONTRIBUTING.md

[macroscopeapp]

Update CONTRIBUTING.md to redirect questions to XMTP Community Forums and simplify bug report and feature request guidance

The CONTRIBUTING.md file redirects user support channels and simplifies contribution guidance:

• Questions section now directs users to XMTP Community Forums at community.xmtp.org instead of GitHub Q&A discussions
• Bug reports section removes detailed instructions about checking existing issues and reproduction steps, directing users specifically to xmtp-ios GitHub Issues page
• Feature requests section removes instructions about checking existing issues and describing use cases, directing users specifically to xmtp-ios GitHub Issues page

📍Where to Start

Start with the questions section in CONTRIBUTING.md to see the redirect from GitHub discussions to XMTP Community Forums.

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Macroscope summarized 9701a11.