add readme 和注释

common_ui/src/main/ets/pages/Index.ets

@@ -0,0 +1,17 @@
+@Entry
+@Component
+struct Index {
+  @State message: string = 'Hello World';
+
+  build() {
+    Row() {
+      Column() {
+        Text(this.message)
+          .fontSize(50)
+          .fontWeight(FontWeight.Bold)
+      }
+      .width('100%')
+    }
+    .height('100%')
+  }
+}

common_ui/src/main/ets/utils/Calc.ets

@@ -0,0 +1,3 @@
+export function add(a:number, b:number) {
+    return a + b;
+}