Updated FAQ (markdown)

FAQ.md

@@ -20,6 +20,7 @@
   * [The first parsing succeeds, why do the next ones fail?](#the-first-parsing-succeeds-why-do-the-next-ones-fail)
   * [Parsing succeeds but I can't read the values!](#parsing-succeeds-but-i-cant-read-the-values)
   * [How to know the type of a value?](#how-to-know-the-type-of-a-value)
+  * [Can I access to object member by its index, instead of its key?](#can-i-access-to-object-member-by-its-index-instead-of-its-key)
   * [How to fix error "Ambiguous overload for 'operator='"](#how-to-fix-error-ambiguous-overload-for-operator)
 
 
@@ -654,6 +655,33 @@ array[0].is<JsonObject&>(); // return false
 See issues [#148](https://github.com/bblanchon/ArduinoJson/issues/148), [#175](https://github.com/bblanchon/ArduinoJson/issues/175) and [#213](https://github.com/bblanchon/ArduinoJson/issues/213).
 
 
+### Can I access to object member by its index, instead of its key?
+
+No.
+
+But you can enumerate all the key-value pairs in the object, by using iterators:
+
+```c++
+char json[] = "{\"key\":\"value\"}";
+JsonObject& object = jsonBuffer.parseObject(json);
+
+for(JsonObject::iterator it=object.begin(); it!=object.end(); ++it) 
+{
+    const char* key = it->key;
+
+    if (it->value.is<char*>()) {        
+        const char* value = it->value;
+        // ...
+    }
+
+    if (it->value.is<JsonObject>()) {
+        JsonObject& value = it->value;
+        // you can recursively traverse objects...
+    }
+}
+```
+
+See issue [#278](https://github.com/bblanchon/ArduinoJson/issues/278).
 
 ### How to fix error "Ambiguous overload for 'operator='"