add: Tencent 404 public welfare page

layouts/404.vue

@@ -1,5 +1,5 @@
 <template>
-  <div class="theme-container">
+  <div class="theme-container" v-if="!noFoundPageByTencent">
     <div class="content">
       <h1>404</h1>
       <blockquote>{{ getMsg() }}</blockquote>
@@ -17,6 +17,21 @@ const msgs = [
 ]
 
 export default {
+  computed: {
+    noFoundPageByTencent () {
+      return this.$themeConfig.noFoundPageByTencent !== false
+    }
+  },
+  mounted () {
+    if (this.noFoundPageByTencent) {
+      let dom = document.createElement('script')
+      dom.setAttribute('homePageName', '回到首页')
+      dom.setAttribute('homePageUrl', '/')
+      dom.setAttribute('src', '//qzonestyle.gtimg.cn/qzone/hybrid/app/404/search_children.js')
+
+      document.body.append(dom)
+    }
+  },
   methods: {
     getMsg () {
       return msgs[Math.floor(Math.random() * msgs.length)]

styles/theme.styl

@@ -217,3 +217,22 @@ th, td
 .vuepress-flowchart
   overflow: auto  
 
+/************** 腾讯 404 公益 **************/
+
+.mod_404 .desc {
+  .desc_link {
+    display: inline-block
+    // margin: 20px 0
+    background: #424242!important
+    color: #ffffff
+    padding: 6px 20px!important
+    text-decoration: none!important
+    border-radius: 4px
+  }  
+}
+
+@media screen and (max-width: 720px) {
+  .mod_404 .desc {
+    margin: 50px 0
+  }  
+}