Update gnss.en.md (#415)

ID list of satellites used

documentation/how-to/gnss.en.md

@@ -242,7 +242,7 @@ The gnss variables always report the gnss sensor values, even when the crosshair
   - `@position_number_of_used_satellites` - Number of satellites as reported by the sensor. It is only
         available when the crosshair is snapped to the sensor. - IE
   - `@position_used_satellites` - A list of satellites in use (pri) as reported by the sensor. It
-        is only available when the crosshair is snapped to the sensor. - `array_length(@position_used_satellites)` - E
+        is only available when the crosshair is snapped to the sensor. - `array_to_string(array_foreach(@position_used_satellites, @element), ', ')` - E
   - `@position_fix_status_description` - The GPS Fix Status "NoData", "NoFix", "Fix2D" or "Fix3D"
         as reported by the sensor. It is only available when the
         crosshair is snapped to the sensor. - E