add doc to DoUpdate where

moor/lib/src/runtime/query_builder/statements/insert.dart

@@ -325,6 +325,11 @@ class DoUpdate<T extends Table, D> extends UpsertClause<T, D> {
   /// If you need to refer to both the old row and the row that would have
   /// been inserted, use [DoUpdate.withExcluded].
   ///
+  /// The optional [where] clause can be used to
+  /// disable the update based on the old value.
+  /// If a [where] clause is set and it evaluates to false,
+  /// a conflict will keep the old row without applying the update
+  ///
   /// For an example, see [InsertStatement.insert].
   DoUpdate(Insertable<D> Function(T old) update,
       {this.target, Expression<bool?> Function(T old)? where})
@@ -340,6 +345,11 @@ class DoUpdate<T extends Table, D> extends UpsertClause<T, D> {
   /// to columns in the row that couldn't be inserted with the `excluded`
   /// parameter.
   /// 
+  /// The optional [where] clause can be used to
+  /// disable the update based on the old value.
+  /// If a [where] clause is set and it evaluates to false,
+  /// a conflict will keep the old row without applying the update
+  /// 
   /// For an example, see [InsertStatement.insert].
   DoUpdate.withExcluded(this._creator,
       {this.target, Expression<bool?> Function(T old, T excluded)? where})