docs(README): Update readme to mention that CloudEvents are read-only now (#248)
docs(README): Update readme to mention that CloudEvents are read-only now (#248)

* also update readme with a mention about the cloneWith method

Signed-off-by: Lucas Holmquist <53dd6492234f115cc187fc638efb40daab835454@redhat.com>
cloudevents/sdk-javascript,cloudevents/sdk-javascript