[Self-Host] Is there doc to introduce how to use the proxy for firecrawl？

[zhucan]

Describe the Issue
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To Reproduce
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2. Run the command '...'
3. Observe the error or unexpected output at '...'
4. Log output/error message

Expected Behavior
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Screenshots
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Environment (please complete the following information):

• OS: [e.g. macOS, Linux, Windows]
• Firecrawl Version: [e.g. 1.2.3]
• Node.js Version: [e.g. 14.x]
• Docker Version (if applicable): [e.g. 20.10.14]
• Database Type and Version: [e.g. PostgreSQL 13.4]

Logs
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Configuration
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Additional Context
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