Update CONTRIBUTING.md

Define the braces position in C++ header files.

CONTRIBUTING.md

@@ -67,7 +67,20 @@ In short: The easier the code review is, the better the chance your pull request
         // Do something
     }
     ```
-
+  However, the method definition could be defined in a header file (.h), if there's one line code only. In this case, Java-like braces should be used.
+  * ###### Good:
+    ```cpp
+    class MyClass
+    {
+    public:
+        void method1();
+        int method2() {
+            return _x; // only one line code can be placed in .h as method definition
+        }
+    private:
+        int _x;
+    }
+    ```
 2. ##### Use tabs instead of white-spaces (we usually set our editors to 4 white-spaces for 1 tab, but the choice is up to you).