docs(model.estimatedDocumentCount): add await into example to get value from the Query

[olecom]

Summary

When doing copy/paste of the example

const numAdventures = Adventure.estimatedDocumentCount();

there is no expected numeric value assigned to the numAdventures. By adding await there will be one.

https://mongoosejs.com/docs/api.html#model_Model.estimatedDocumentCount

[vkarpov15]

Thanks 👍