Update non-local impl definition lint rule note

Author: Urgau

compiler/rustc_lint/messages.ftl

@@ -443,7 +443,7 @@ lint_non_local_definitions_impl = non-local `impl` definition, they should be av
             [one] `{$body_name}`
            *[other] `{$body_name}` and up {$depth} bodies
         }
-    .non_local = an `impl` definition is non-local if it is nested inside an item and neither the type nor the trait are at the same nesting level as the `impl` block
+    .non_local = an `impl` definition is non-local if it is nested inside an item and may impact type checking outside of that item. This can be the case if neither the trait or the self type are at the same nesting level as the `impl`
     .exception = one exception to the rule are anon-const (`const _: () = {"{"} ... {"}"}`) at top-level module and anon-const at the same nesting as the trait or type
     .const_anon = use a const-anon item to suppress this lint