Add Decoration Files in package.json

Author: climba03003

package.json

@@ -20,9 +20,11 @@
     "url": "https://github.com/woocommerce/woocommerce-rest-api-js/issues"
   },
   "main": "index",
+  "types": "index.d.ts",
   "files": [
     "index.js",
-    "index.mjs"
+    "index.mjs",
+    "index.d.ts"
   ],
   "dependencies": {
     "axios": "^0.19.0",