add README to graph (#1211)

### What problem does this PR solve?


### Type of change

- [x] Documentation Update

graph/test/dsl_examples/customer_service.json

@@ -4,7 +4,7 @@
                 "obj":{
                     "component_name": "Begin",
                     "params": {
-                      "prologue": "Hi there!"
+                      "prologue": "Hi! How can I help you?"
                     }
                 },
                 "downstream": ["answer:0"],