docs: Adding an example for ConversationHistory (#1302)

examples/conversation_history/conversation_history.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/slack-go/slack"
+)
+
+func main() {
+	api := slack.New("YOUR_TOKEN")
+	params := slack.GetConversationHistoryParameters{
+		ChannelID: "C0123456789",
+	}
+	messages, err := api.GetConversationHistoryContext(context.Background(), &params)
+	if err != nil {
+		fmt.Printf("%s\n", err)
+		return
+	}
+	for _, message := range messages.Messages {
+		fmt.Printf("Message: %s\n", message.Attachments[0].Color)
+	}
+}