@Karla180,
If your Wifi has limitations due to the area you live in, maybe mention it in your listing.
But as with everything provided: guest should use it in a fair way. If the use is excessive, you can ask them to limit (or pay for overuse, if your provider going to charge you for that). Continous streaming of videos etc. by one guests can, besides the high amount of transferred data, also limit you and other guests in accessing the Internet. A guest should be able to understand this.