docs: update embind code sample comment (#5604)

`incrementX` only adds by 1.

Author: rebornix

site/source/docs/porting/connecting_cpp_and_javascript/embind.rst

@@ -150,7 +150,7 @@ shown below:
 
    var instance = new Module.MyClass(10, "hello");
    instance.incrementX();
-   instance.x; // 12
+   instance.x; // 11
    instance.x = 20; // 20
    Module.MyClass.getStringFromInstance(instance); // "hello"
    instance.delete();