trunc contrubuting note

CONTRIBUTING.md

@@ -72,6 +72,7 @@ https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects
 - Take care of `int` -> `number` (integer to number) port when doing bitwise transformation especially `<<`. Do a `& 0xFFFFFFFF` for ints, a &0xFF for bytes.
 - Take care of array initialization, in Java `new Array(N)` initializes capacity NOT size/length.
 - Use `Math.floor` for any division of ints otherwise the `number` type is a floating point and keeps the numbers after the dot.
+- For `float` to `int` casting use `Math.trunc`, to replicate the same effect as Java casting does.
 
 ## Encoding