To me it just looks like a small nick which isn't too serious. You need to keep it from getting infected though.
1) Clean and disinfect the cage daily.
2) Remove substrate and use clean newspaper or paper towels.
3) Dilute betadine soak of tail tip about 5 to 10 mins daily.
4) Apply triple antibiotic ointment like neosporin daily after betadine. I personally found manuka honey to work better than antibiotic ointments, if you decide to try this, make sure it says UMF on the label (not just "active" or some other term.) and a rating of about 15+ or 18+.
It probably will heal on itself but I would do this to be safe.
If it gets worse see a vet.