readme: Add quickstart sample code to readme

README.md

@@ -2,3 +2,55 @@
 
 [![go.dev reference](https://img.shields.io/badge/go.dev-reference-007d9c?logo=go&logoColor=white&style=flat-square)](https://pkg.go.dev/github.com/tmc/langgraphgo)
 
+
+## Quick Start
+
+
+This is a simple example of how to use the library to create a simple chatbot that uses OpenAI to generate responses.
+
+```go
+func ExampleMessageGraph() {
+	model, err := openai.New()
+	if err != nil {
+		panic(err)
+	}
+
+	g := graph.NewMessageGraph()
+
+	g.AddNode("oracle", func(ctx context.Context, state []llms.MessageContent) ([]llms.MessageContent, error) {
+		r, err := model.GenerateContent(ctx, state, llms.WithTemperature(0.0))
+		if err != nil {
+			return nil, err
+		}
+		return append(state,
+			llms.TextParts(schema.ChatMessageTypeAI, r.Choices[0].Content),
+		), nil
+
+	})
+	g.AddNode(graph.END, func(ctx context.Context, state []llms.MessageContent) ([]llms.MessageContent, error) {
+		return state, nil
+	})
+
+	g.AddEdge("oracle", graph.END)
+	g.SetEntryPoint("oracle")
+
+	runnable, err := g.Compile()
+	if err != nil {
+		panic(err)
+	}
+
+	ctx := context.Background()
+	// Let's run it!
+	res, err := runnable.Invoke(ctx, []llms.MessageContent{
+		llms.TextParts(schema.ChatMessageTypeHuman, "What is 1 + 1?"),
+	})
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Println(res)
+
+	// Output:
+	// [{human [{What is 1 + 1?}]} {ai [{1 + 1 equals 2.}]}]
+}
+```