If you want more people on Facebook to see your Campsite.bio profile URL, you'll have to make sure your profile is set to public, but this isn't a requirement.
On desktop
Go to your Facebook profile
Directly below your profile image, select "Edit bio"
Paste your Campsite URL
Click save
On the mobile app
Open the Facebook app
Open the main menu and select your profile
Beneath your name, paste your Campsite URL into the Edit bio field