message: docs(guide): add snap function args
diff: @@ -150,9 +150,23 @@ modifiers. If multiple targets are within range, the closest target is used.
  ```js
  interact.modifiers.snap({
  - targets: [(x, y) => {
  - return { x: x * 2, y: y +100 }
  - }]
  + targets: [
  + function (
  + // the x and y page coordinates,
  + x, y,
  + // the current interaction
  + interaction,
  + // the offset information with relativePoint if set
  + { x: offsetX, y: offsetY, relativePoint, index: relativePointIndex },
  + // the index of this function in the options.targets array
  + index) {
  + return {
  + x: x,
  + y: (75 + 50 * Math.sin(x * 0.04)),
  + range: 40,
  + }
  + }
  + ]
  })
  ```
  