Yes there is, and it pops up about 20 seconds into the game. However, its text could certainly use an update – especially considering potions can’t be purchased from vendors.
Perhaps it could instead say something like this:
You’re taking damage! Use health potions to restore your health. Health potions drop from killing enemies or hitting bosses and the number of potions you can carry is tied directly to your belt.
OR it could end with; the number of potions you can carry is dependent on your belt.
And then also have a link to the Potions section of the Game Guide for those that want further information.