Updated FAQ (markdown)

FAQ.md

@@ -260,6 +260,25 @@ array[0].is<JsonObject&>(); // return false
 
 See issues [#148](https://github.com/bblanchon/ArduinoJson/issues/148) and [#175](https://github.com/bblanchon/ArduinoJson/issues/175).
 
+### How to write a function that works with both `JsonArray` and `JsonObject`?
+
+There is no base class for `JsonArray` and `JsonObject`.
+(Back in version 3.0, they used to derive from `Printable`, but this inheritance has been removed to reduce the memory footprint.)
+
+However, both `JsonArray` and `JsonObject` can be "stored" in a `JsonVariant`. (I put "stored" in quotes because the `JsonVariant` only contains a reference, not a copy.)
+
+So here is your function:
+
+```c++
+void sendJson(JsonVariant json) {
+    char buffer[512];
+    json.printTo(buffer, sizeof(buffer));
+    g_server.send(200, "application/json", buffer);
+}
+```
+
+See issue [#195](https://github.com/bblanchon/ArduinoJson/issues/195)
+
 ### What are the differences between `StaticJsonBuffer` and `DynamicJsonBuffer`?
 
                  | `StaticJsonBuffer`  | `DynamicJsonBuffer`