Add the Bunun language

The people from the Taiwan Center for Aboriginal Studies
asked to add this. They plan to create a Wikipedia in it,
as a follow-up to the successful Atayal (tay) and Sakizaya (ais) projects.

data/langdb.yaml

@@ -72,6 +72,7 @@ languages:
   bjn: [Latn, [AS], Bahasa Banjar]
   bm: [Latn, [AF], bamanankan]
   bn: [Beng, [AS], বাংলা]
+  bnn: [Latn, [AS], Bunun]
   bo: [Tibt, [AS], བོད་ཡིག]
   bpy: [Beng, [AS], বিষ্ণুপ্রিয়া মণিপুরী]
   bqi: [Arab, [AS, ME], بختیاری]