Document link between import-outside-top-level (PLC0415) and lint.flake8-tidy-imports.banned-module-level-imports (#18733)

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## Summary

As mentioned in
https://github.com/astral-sh/ruff/issues/18728#issuecomment-2981330666
CC @ntBre


![image](https://github.com/user-attachments/assets/ac0e9ea6-6510-48be-b775-47b30bdf7efe)

![image](https://github.com/user-attachments/assets/2a69df6f-1973-4d81-8985-9e0ce70f8175)


## Test Plan

Run the docs locally as per
a2cd6df429/CONTRIBUTING.md (mkdocs)

---------

Co-authored-by: Brent Westbrook <brentrwestbrook@gmail.com>

crates/ruff_workspace/src/options.rs

@@ -1996,7 +1996,8 @@ pub struct Flake8TidyImportsOptions {
 
     /// List of specific modules that may not be imported at module level, and should instead be
     /// imported lazily (e.g., within a function definition, or an `if TYPE_CHECKING:`
-    /// block, or some other nested context).
+    /// block, or some other nested context). This also affects the rule `import-outside-top-level`
+    /// if `banned-module-level-imports` is enabled.
     #[option(
         default = r#"[]"#,
         value_type = r#"list[str]"#,