small docs update

Author: gfwilliams

src/jswrap_io.c

@@ -721,7 +721,7 @@ information (all optional):
    // setting irq:true will call that function in the interrupt itself
    irq : false(default)
    // Advanced: If specified, the given pin will be read whenever the watch is called
-   // and the state will be included as a 'data' field in the callback
+   // and the state will be included as a 'data' field in the callback (`debounce:0` is required)
    data : pin
    // Advanced: On Nordic devices, a watch may be 'high' or 'low' accuracy. By default low
    // accuracy is used (which is better for power consumption), but this means that
@@ -740,7 +740,7 @@ The `function` callback is called with an argument, which is an object of type
    When using `edge:'rising'` or `edge:'falling'`, this is not the same as when
    the function was last called.
  * `data` is included if `data:pin` was specified in the options, and can be
-   used for reading in clocked data
+   used for reading in clocked data. It will only work if `debounce:0` is used
 
 For instance, if you want to measure the length of a positive pulse you could
 use `setWatch(function(e) { console.log(e.time-e.lastTime); }, BTN, {