Improve rules configuration docs

[tigitz]

Hello,

I've noticed that the current documentation for Rector rules only shows the configuration setup, but it doesn't explain the purpose of the configuration values. This forces me to open the rule directly in my IDE to understand the details.

For example, this page: https://getrector.com/rule-detail/class-property-assign-to-constructor-promotion-rector

It might be useful to automatically parse the relevant information from the Rule file and inject it into the documentation. Could improve DX, especially during project setup.