feat(Steps): desc properties add custom style (#2630)

* feat(Steps): steps add custom style

* feat(Steps): steps add custom style

packages/steps/README.md

@@ -88,3 +88,4 @@ Page({
 | 类名 | 说明 |
 |-----------|-----------|
 | custom-class | 根节点样式类 |
+| desc-class | 描述信息样式类 |

packages/steps/index.ts

@@ -2,6 +2,8 @@ import { VantComponent } from '../common/component';
 import { GREEN, GRAY_DARK } from '../common/color';
 
 VantComponent({
+  classes: ['desc-class'],
+
   props: {
     icon: String,
     steps: Array,

packages/steps/index.wxml

@@ -10,7 +10,7 @@
     >
       <view class="van-step__title" style="{{ index === active ? 'color: ' + activeColor : '' }}">
         <view>{{ item.text }}</view>
-        <view>{{ item.desc }}</view>
+        <view class="desc-class">{{ item.desc }}</view>
       </view>
       <view class="van-step__circle-container">
         <block wx:if="{{ index !== active }}">