update(README): add link to SDK usage example
update(README): add link to SDK usage example

Related to: CAM-3114
camunda/camunda-bpm-sdk-js,lightswitch05/camunda-bpm-sdk-js,camunda/camunda-bpm-sdk-js,lightswitch05/camunda-bpm-sdk-js,nagyistoce/camunda-bpm-sdk-js,nagyistoce/camunda-bpm-sdk-js