feat: publicize doc implemetation

one/docs/demo/overlay/stack-on-overlay.vue

@@ -0,0 +1,69 @@
+<template>
+<article>
+  <veui-button
+    ref="parent"
+    @click="parentOpen = !parentOpen"
+  >
+    Toggle
+  </veui-button>
+  <veui-overlay
+    target="parent"
+    position="top-start"
+    :open.sync="parentOpen"
+    overlay-class="relative-overlay"
+  >
+    <veui-button
+      ref="child"
+      @click="childOpen = !childOpen"
+    >
+      Toggle
+    </veui-button>
+    <veui-overlay
+      target="child"
+      position="top-start"
+      :open.sync="childOpen"
+      overlay-class="relative-overlay"
+    >
+      Child Overlay
+    </veui-overlay>
+  </veui-overlay>
+  <veui-button
+    ui="xs"
+    @click="parentOpen = childOpen = false"
+  >
+    Hide all
+  </veui-button>
+</article>
+</template>
+
+<script>
+import { Overlay, Button } from 'veui'
+
+export default {
+  components: {
+    'veui-overlay': Overlay,
+    'veui-button': Button
+  },
+  data () {
+    return {
+      parentOpen: false,
+      childOpen: false
+    }
+  },
+  watch: {
+    parentOpen (val) {
+      if (!val) {
+        this.childOpen = false
+      }
+    }
+  }
+}
+</script>
+
+<style lang="less" docs scoped>
+.veui-button {
+  margin-right: 10px;
+}
+</style>
+
+<style lang="less" src="./relative.less" docs></style>