doc: Link starter kit doc to youtube video

[vlasebian]

Summary

Adding a link in the Starter Kit section to the YouTube video guide.

Screenshots

Changes

• Add youtube link under toggle
• Move paragraph

Notes for Reviewers

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Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Run Locally: Verified that the docs build using make server, posted screenshots, verified external links. Test with HUGO_PARAMS_SEARCH_ENABLED=true if style changes will affect the search bar.
• New Features Marked: Documentation for new features is marked using the new-in-version shortcode, according to the guidelines in CONTRIBUTING.
• Style Guidelines: Documentation obeys style guidelines in CONTRIBUTING.
• Commits: Commit messages follow guidelines in CONTRIBUTING, there are no fixup commits left.

[Copilot]

Pull Request Overview

This PR adds a YouTube video guide link to the Starter Kit documentation section. The changes improve user experience by providing both text-based and video-based learning options for getting started with the kit.

Key changes:

• Add YouTube video link in a collapsible details section
• Reorganize paragraph content for better flow

Comments suppressed due to low confidence (1)

doc/content/getting-started/3-try-starter-kit/activate/_index.md:17

• The word 'needed' appears to be truncated at the end of line 17. It shows 'neede' instead of 'needed'.

First, set up the gateway. It receives messages from the end device and forwards them to {{% tts %}}, and the other way around. Once the gateway is online, you can activate your end device to start sending and receiving data.