[docs] Reduce extend-aliases note to the override behavior

Per review, keep the change minimal and just acknowledge that entries
override an overlapping `aliases` entry, rather than presenting the
self-alias trick as a recommended way to opt out of a default.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: LHMQ878

crates/ruff_workspace/src/options.rs

@@ -1623,21 +1623,15 @@ pub struct Flake8ImportConventionsOptions {
     pub aliases: Option<FxHashMap<ModuleName, Alias>>,
 
     /// A mapping from module to conventional import alias. These aliases will
-    /// be added to the [`aliases`](#lint_flake8-import-conventions_aliases) mapping.
-    ///
-    /// Entries here take precedence over [`aliases`](#lint_flake8-import-conventions_aliases),
-    /// so this option can also be used to change or opt out of a default alias without
-    /// restating the entire mapping. Mapping a module to its own name requires it to be
-    /// imported unaliased.
+    /// be added to the [`aliases`](#lint_flake8-import-conventions_aliases) mapping
+    /// and will override any existing `aliases` if the two settings overlap.
     #[option(
         default = r#"{}"#,
         value_type = "dict[str, str]",
         scope = "extend-aliases",
         example = r#"
             # Declare a custom alias for the `dask` module.
             "dask.dataframe" = "dd"
-            # Require `numpy` to be imported unaliased, overriding the default `np` alias.
-            numpy = "numpy"
         "#
     )]
     pub extend_aliases: Option<FxHashMap<ModuleName, Alias>>,