docs: correct sidebar and copy block comments

[zoupingcenter]

Summary

• Correct the sidebar comment to match the /docs/platforms path check.
• Describe CopyBlock as a copyable snippet, since it displays more than command lines.

[stellar-triage-bot]

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[kaankacar]

/triage

[stellar-triage-bot]

🤖 Automated message from the Stellar Triage Bot.

Reviewing because @kaankacar asked with /triage.

Verified: both comments now match the code. The sidebar check uses /docs/platforms, and CopyBlock also shows JSON configs, URLs and a prompt. Ready to merge.

• No live preview was available. "Build, format MDX and Lint" is held at action_required (first-time fork contributor). Please approve that run before you merge.
• External-origin change, so a maintainer merges this.