fix docs

Author: alamb

datafusion/physical-expr/src/window/built_in_window_function_expr.rs

@@ -76,10 +76,10 @@ pub trait BuiltInWindowFunctionExpr: Send + Sync + std::fmt::Debug {
         None
     }
 
-    /// Adds any equivalent orderings this expression expression
-    /// generates to the `builder`.
+    /// Adds any equivalent orderings generated by this expression
+    /// to `builder`.
     ///
-    /// by default does nothing
+    /// The default implementation does nothing
     fn add_equal_orderings(&self, _builder: &mut OrderingEquivalenceBuilder) {}
 
     /// Can the window function be incrementally computed using