Refine and modernize Apache Kafka website introductionDocs update intro

[Rafiaminhaj]

What does this PR do?

This PR improves the Apache Kafka website introduction page by refining the wording,
structure, and readability of the content.

The goal is to make the introduction clearer and more approachable for:

• New users
• Students
• First-time contributors

What was changed?

• Improved clarity and flow of the introductory text
• Minor content refinements for better readability
• Maintained existing structure and messaging consistency

Why is this change needed?

Clear and accessible documentation is essential for onboarding new users
and contributors. These improvements help users quickly understand
Apache Kafka’s purpose and core capabilities.

Additional notes

• No functional or code changes are included
• Changes are documentation-only