Improve NewRoundTripper guide example
@@ -335,6 +335,7 @@ ways to use this functionality:
client := &http.Client{}
client.Transport = newrelic.NewRoundTripper(client.Transport)
request, _ := http.NewRequest("GET", "http://example.com", nil)
+ // Put transaction in the request's context:
request = newrelic.RequestWithTransactionContext(request, txn)
resp, err := client.Do(request)
```
