docs(query): clarify that orFail() with updateX() throws if no do…

…cument updated, not if no document found

Re: #11620

lib/query.js

@@ -4610,7 +4610,10 @@ Query.prototype.transform = function(fn) {
  *     // Throws if no doc returned
  *     await Model.findOne({ foo: 'bar' }).orFail();
  *
- *     // Throws if no document was updated
+ *     // Throws if no document was updated. Note that `orFail()` will still
+ *     // throw if the only document that matches is `{ foo: 'bar', name: 'test' }`,
+ *     // because `orFail()` will throw if no document was _updated_, not
+ *     // if no document was _found_.
  *     await Model.updateOne({ foo: 'bar' }, { name: 'test' }).orFail();
  *
  *     // Throws "No docs found!" error if no docs match `{ foo: 'bar' }`