Update readme with example

Author: zph

README.md

@@ -1,2 +1,40 @@
 # bayeux
-Bayeux Client Protocol (as specified by Salesforce Realtime API)
+Bayeux Client Protocol implemented in Golang (as specified by Salesforce Realtime API)
+
+# Usage
+See `examples/main.go`
+```golang
+package main
+
+import (
+	"fmt"
+
+	bay "github.com/zph/bayeux"
+)
+
+func Example() {
+	b := bay.Bayeux{}
+	creds := bay.GetSalesforceCredentials()
+	c := b.TopicToChannel(creds, "topicName")
+	for {
+		select {
+		case e := <-c:
+			fmt.Printf("TriggerEvent Received: %+v", e)
+		}
+	}
+}
+
+func main() {
+	Example()
+}
+```
+
+See annotations in code for cases where the Salesforce implementation of Bayeux seems to differ from official spec.
+
+Salesforce documentation on Realtime API: https://resources.docs.salesforce.com/sfdc/pdf/api_streaming.pdf
+
+# Stability
+
+This code or variant thereof has been steadily running in production since Nov 2016.
+
+The API is very new. So only a few functions are exposed publicly and these can be expected to remain stable until 12/2018, pending massive changes to Salesforce API. Reasonable attempts will be made to maintain API past that deadline.