Duplicates detection: installation + basic usage + available configuration options

[mrtnzlml]

The goal of this issue is to complete the following page: https://rossum.university/docs/learn/duplicates-detection

Specifically:

• Finish section "Installation"
• Finish section "Basic usage" (describe a minimal example of how to use the extension)
• Finish section "Available configuration options" (describe what are the configuration options of the extension); for inspiration, many of the options are described here: https://rossum.ai/help/article/duplicate-handling-extension/

Remember: keep it simple. 😎

Please visit other similar pages to keep the style unified. For example: https://rossum.university/docs/learn/business-rules-validation