add _vercel.koa.json for vercel txt verification

domains/_vercel.koa.json

@@ -0,0 +1,10 @@
+{
+  "owner": {
+    "username": "koaexe"
+  },
+  "records": {
+    "TXT": [
+      "vc-domain-verify=koa.is-a.dev,6f0ccfa1f8b4330dfeb3"
+    ]
+  }
+}