Add a `triggerEvent` doc example

[yannbertrand]

My team and I have been struggling with the triggerEvent options parameter.

Our usecase is fixing a Firefox bug where the mouseleave event is triggered when hovering a select option even if the mouse is still hover the target element. We did some acceptance tests to trigger the event with or without a given relatedTarget element.

Hopefully this PR will help other users too 😄.

[rwjblue]

Looks like some linting failures here (sorry for taking so long to approve the run) @yannbertrand

[yannbertrand]

Looks like some linting failures here (sorry for taking so long to approve the run) @yannbertrand

Should be fixed now. Thank you for your patience :)