docs(webex-core): update readme
docs(webex-core): update readme

Update the readme to include details in regards to the
newly added features. These features should include
and updated example and env usage notes.

adamweeks/spark-js-sdk,mwegman/spark-js-sdk,mwegman/spark-js-sdk,aimeex3/spark-js-sdk,mwegman/spark-js-sdk,adamweeks/spark-js-sdk,adamweeks/spark-js-sdk,aimeex3/spark-js-sdk,aimeex3/spark-js-sdk