feat: watermark (#203)

* feat: add watermark

src/views/able/watermark.vue

@@ -0,0 +1,13 @@
+<script setup lang="ts">
+import { useWatermark } from "/@/utils/watermark";
+const { setWatermark, clear } = useWatermark();
+</script>
+
+<template>
+  <div>
+    <el-button @click="setWatermark('vue-pure-admin')">创建</el-button>
+    <el-button @click="clear">清除</el-button>
+  </div>
+</template>
+
+<style scoped></style>