chore: Update readme with correct Receiver usage (#287)

Signed-off-by: Lucas Holmquist <lholmqui@redhat.com>

README.md

@@ -39,11 +39,8 @@ const {
   Receiver
 } = require("cloudevents");
 
-// Create a receiver to accept events over HTTP
-const receiver = new Receiver();
-
 // body and headers come from an incoming HTTP request, e.g. express.js
-const receivedEvent = receiver.accept(req.headers, req.body);
+const receivedEvent = Receiver.accept(req.headers, req.body);
 console.log(receivedEvent);
 ```
 
@@ -157,4 +154,4 @@ We love contributions from the community! Please check the
 for information on how to get involved.
 
 [v1spec]: https://github.com/cloudevents/spec/tree/v1.0
-[v103pec]: https://github.com/cloudevents/spec/tree/v0.3
+[v103pec]: https://github.com/cloudevents/spec/tree/v0.3