update readme - missing keys example

Author: Perlmint

README.md

@@ -46,4 +46,14 @@ if (window._t === undefined) {
 }
 
 console.log(_t("hello_world"));
+```
+
+## example missing keys
+
+```json
+{
+	"hello_world": [
+		"index.js(18,16)"
+	],
+}
 ```