docs(aggregate): make aggregation Symbol.iterator docs actually use a…

…ggregate()

Re: #8280

lib/aggregate.js

@@ -1011,20 +1011,20 @@ Aggregate.prototype.catch = function(reject) {
 
 /**
  * Returns an asyncIterator for use with [`for/await/of` loops](http://bit.ly/async-iterators)
- * This function *only* works for `find()` queries.
  * You do not need to call this function explicitly, the JavaScript runtime
  * will call it for you.
  *
  * ####Example
  *
- *     for await (const doc of Model.find().sort({ name: 1 })) {
+ *     const agg = Model.aggregate([{ $match: { age: { $gte: 25 } } }]);
+ *     for await (const doc of agg) {
  *       console.log(doc.name);
  *     }
  *
  * Node.js 10.x supports async iterators natively without any flags. You can
  * enable async iterators in Node.js 8.x using the [`--harmony_async_iteration` flag](https://github.com/tc39/proposal-async-iteration/issues/117#issuecomment-346695187).
  *
- * **Note:** This function is not if `Symbol.asyncIterator` is undefined. If
+ * **Note:** This function is not set if `Symbol.asyncIterator` is undefined. If
  * `Symbol.asyncIterator` is undefined, that means your Node.js version does not
  * support async iterators.
  *