Add documentation examples for filtering expressions

[alexgQQ]

Hello again 👋

Glad you found use from the filtering functionality in my previous PR . This just adds some example uses for the filtering in the docs application you have. Let me know your thoughts when you get a chance.

I'd be curious on your thoughts of some nested filtering functionality too. With this current setup, you can filter on direct values for the requested data model. A neat feature would be something like /quotes?character_name='Gandalf'. It would take some hacking, we'd need to figure some functions to cast it (https://github.com/leodinas-hao/mongoose-query-parser#add-custom-casting-functions) but if it would be useful we can give it a shot

Happy #hacktoberfest 🎉

[gitfrosh]

Hi there,
thanks again for your contribution, really great! I added some minor changes and will merge your PR.
Let's definitely have a look into nested filtering functionality! Feel free to open a PR whenever you like.
Cheers 🍾