chore: add licence field

Author: cat394

deno.json

@@ -5,5 +5,6 @@
   "imports": {
     "@std/assert": "jsr:@std/assert@^1.0.2",
     "@std/testing": "jsr:@std/testing@^1.0.0"
-  }
+  },
+  "license": "MIT"
 }