docs: improve docs and update api

one/docs/demo/directives/tooltip/default.vue

@@ -0,0 +1,45 @@
+<template>
+<article>
+  <veui-button
+    v-tooltip="'Preview'"
+    ui="icon"
+  >
+    <veui-icon name="zoom-in"/>
+  </veui-button>
+  <veui-button
+    v-tooltip="'Upload'"
+    ui="icon"
+  >
+    <veui-icon name="upload"/>
+  </veui-button>
+  <veui-button
+    v-tooltip="'Remove'"
+    ui="icon"
+  >
+    <veui-icon name="trash"/>
+  </veui-button>
+</article>
+</template>
+
+<script>
+import { Button, Icon, tooltip } from 'veui'
+import 'veui-theme-dls-icons/zoom-in'
+import 'veui-theme-dls-icons/upload'
+import 'veui-theme-dls-icons/trash'
+
+export default {
+  components: {
+    'veui-button': Button,
+    'veui-icon': Icon
+  },
+  directives: {
+    tooltip
+  }
+}
+</script>
+
+<style lang="less" scoped>
+.veui-button + .veui-button {
+  margin-left: 8px;
+}
+</style>