Updated FAQ (markdown)

FAQ.md

@@ -14,6 +14,24 @@ If you're is case 2., you can solve the problem by increasing the size of the `S
 
 If you're in case 3., you may have a memory leak, it up to you to find it. You can try to switch to `StaticJsonBuffer` which is more efficient.
 
+Also, if the input string is constant, the `JsonBuffer` will have to make a copy of it.
+
+```c++
+// case 1: char array => no duplication => good
+char[] json = "{\"hello\":\"world\"}";
+jsonBuffer.parseObject(json);
+
+// case 2: const char* => duplication => bad
+const char* json = "{\"hello\":\"world\"}";
+jsonBuffer.parseObject(json);
+
+// case 3: String => duplication => bad
+String json = "{\"hello\":\"world\"}";
+jsonBuffer.parseObject(json);
+```
+
+To avoid any duplication, make sure you use an input of type `char*` or `char[]`
+
 ### The first parsing succeeds, why does the next ones fail?
 
 This can be due to two causes.