docs: rewrite README; feat: dark login bg, svg logo, avatar fallback

src/components/main/components/user/user.vue

@@ -2,7 +2,7 @@
   <div class="user-avator-dropdown">
     <Dropdown @on-click="handleClick">
       <span style="font-size: 15px;font-weight: bold"> {{ nickname }} </span>
-      <Avatar :src="userAvator"/>
+      <Avatar :key="userAvator" :src="userAvator" style="background-color: #2d8cf0; vertical-align: middle">{{ avatarText }}</Avatar>
       <Icon :size="18" type="md-arrow-dropdown"></Icon>
       <DropdownMenu slot="list">
         <DropdownItem name="personal-center">个人中心</DropdownItem>
@@ -27,6 +27,12 @@ export default {
       default: ''
     }
   },
+  computed: {
+    avatarText () {
+      const name = (this.nickname || '').trim()
+      return name ? name.charAt(0) : 'U'
+    }
+  },
   methods: {
     ...mapActions([
       'handleLogOut'

src/components/main/main.less

@@ -2,6 +2,7 @@
   .logo-con{
     height: 64px;
     padding: 10px;
+    text-align: center;
     img{
       height: 44px;
       width: auto;

src/components/main/main.vue

@@ -41,8 +41,8 @@ import Fullscreen from './components/fullscreen'
 import ErrorStore from './components/error-store'
 import { mapMutations, mapActions, mapGetters } from 'vuex'
 import { getNewTagList, getNextRoute, routeEqual } from '@/libs/util'
-import minLogo from '@/assets/images/logo-min.jpg'
-import maxLogo from '@/assets/images/logo.jpg'
+import minLogo from '@/assets/images/logo-min.svg'
+import maxLogo from '@/assets/images/logo.svg'
 import './main.less'
 export default {
   name: 'Main',