[ENG-3611] docs: vercel secret sync info

[gupta-piyush19]

Description 📣

vercel secret sync info

Type ✨

• Bug fix
• New feature
• Improvement
• Breaking change
• Documentation

Tests 🛠️

# Here's some code block to paste some code snippets

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[maidul98]

✅ Snyk checks have passed. No issues have been found so far.

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[greptile-apps]

Greptile Summary

• Added documentation note explaining how to handle Vercel's sensitive environment variables feature during secret syncing
• Included link to Vercel's official documentation for sensitive environment variables

Confidence Score: 5/5

• This documentation change is safe to merge with no risk
• This is a pure documentation enhancement that adds valuable information about a Vercel platform limitation. No code changes, no breaking changes, and improves user experience by preemptively addressing a common issue users may encounter.
• No files require special attention

[greptile-apps]

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