add sample code

README.md

@@ -1,3 +1,55 @@
 # EasyNodeEditor
 
-Very easy node editor.
+```.swift
+import SwiftUI
+import EasyNodeEditor
+
+struct ContentView: View {
+    var body: some View {
+        EasyNodeEditor(nodeTypes: [Output3Node.self, MultiplyNode.self, ShowNode.self])
+    }
+}
+
+class Output3Node: NodeModelBase {
+    @objc @Output var output: Int = 3
+}
+
+class MultiplyNodeSubModel: ObservableObject {
+    @Published var sliderValue: Double = 0.0
+}
+class MultiplyNode: NodeModelBase {
+    @objc @Input var input: Int = 0
+    @ObservedObject var subModel = MultiplyNodeSubModel()
+    @objc @Middle var count: Int = 0
+    @objc @Output var output: Int = 0
+    override func processOnChange() {
+        output = input * count
+    }
+    override func middleContent() -> AnyView {
+        return AnyView(
+            Group {
+                Slider(value: self.$subModel.sliderValue, in: 0...100, onEditingChanged: { changed in
+                    self.count = Int(self.subModel.sliderValue)
+                })
+            }
+            .frame(minWidth: 200, maxWidth: 200)
+            .fixedSize()
+        )
+    }
+}
+
+class ShowNode: NodeModelBase {
+    @objc @Input var myinput: Int = 0
+    var showCount = 0
+    override func processOnChange() {
+        showCount = myinput
+    }
+    override func middleContent() -> AnyView {
+        return AnyView(
+            Group {
+                Text("number is now -> \(showCount)")
+            }
+        )
+    }
+}
+```