update readme

Author: hackw

README.md

@@ -108,18 +108,18 @@ class ExampleState extends State<Example> {
   double x = 0;
   double y = 0;
 
-  ConstraintId box0 = ConstraintId();
-  ConstraintId box1 = ConstraintId();
-  ConstraintId box2 = ConstraintId();
-  ConstraintId box3 = ConstraintId();
-  ConstraintId box4 = ConstraintId();
-  ConstraintId box5 = ConstraintId();
-  ConstraintId box6 = ConstraintId();
-  ConstraintId box7 = ConstraintId();
-  ConstraintId box8 = ConstraintId();
-  ConstraintId box9 = ConstraintId();
-  ConstraintId box10 = ConstraintId();
-  ConstraintId box11 = ConstraintId();
+  ConstraintId box0 = ConstraintId('box0');
+  ConstraintId box1 = ConstraintId('box1');
+  ConstraintId box2 = ConstraintId('box2');
+  ConstraintId box3 = ConstraintId('box3');
+  ConstraintId box4 = ConstraintId('box4');
+  ConstraintId box5 = ConstraintId('box5');
+  ConstraintId box6 = ConstraintId('box6');
+  ConstraintId box7 = ConstraintId('box7');
+  ConstraintId box8 = ConstraintId('box8');
+  ConstraintId box9 = ConstraintId('box9');
+  ConstraintId box10 = ConstraintId('box10');
+  ConstraintId box11 = ConstraintId('box11');
 
   @override
   Widget build(BuildContext context) {
@@ -325,7 +325,7 @@ class GuidelineExample extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    ConstraintId guideline = ConstraintId();
+    ConstraintId guideline = ConstraintId('guideline');
     return MaterialApp(
       home: Scaffold(
         body: ConstraintLayout(
@@ -384,9 +384,9 @@ class BarrierExample extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    ConstraintId leftChild = ConstraintId();
-    ConstraintId rightChild = ConstraintId();
-    ConstraintId barrier = ConstraintId();
+    ConstraintId leftChild = ConstraintId('leftChild');
+    ConstraintId rightChild = ConstraintId('rightChild');
+    ConstraintId barrier = ConstraintId('barrier');
     return MaterialApp(
       home: Scaffold(
         body: ConstraintLayout(
@@ -452,7 +452,7 @@ class BadgeExample extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    ConstraintId anchor = ConstraintId();
+    ConstraintId anchor = ConstraintId('anchor');
     return MaterialApp(
       home: Scaffold(
         body: ConstraintLayout(