Add event listener documentation for opc-timeline

[hybridx]

• op-components/packages/opc-timeline/demo/index.html

  Line 66 in 515069b

  el.addEventListener('opc-timeline-step:click', (e) => {console.log(e)});

Is your chore related to a problem? Please describe

• Event listener documentation not available for timeline component

Describe the solution you'd like

• A clear and concise description of how to use the event listener for opc-timeline

Describe alternatives you've considered

• None

Additional context

• None