[Doc] add custom Icon directions (#754)

docs/markdown/en-US/icon.md

@@ -23,6 +23,36 @@ Icon uses font file in `yzcdn.cn` by default，if you want to use the local font
 import 'vant/lib/vant-css/icon-local.css';
 ```
 
+#### Use custom font
+Add more custom icon
+
+[Demo](https://github.com/qianzhaoy/vant--mobile-mall/blob/master/src/assets/scss/iconfont/iconfont.css)
+
+```css
+@font-face {
+	font-family: "iconfont";
+	src: url('./iconfont.ttf') format('truetype');
+}
+
+@font-face {
+	font-family: "vanIcon";
+	src: url(https://b.yzcdn.cn/zanui/icon/vant-icon-4c3245.ttf) format('truetype');
+}
+
+.van-icon {
+	position: relative;
+	font-family: "iconfont", "vanIcon" !important;
+	font-size: 14px;
+	font-style: normal;
+	-webkit-font-smoothing: antialiased;
+	-moz-osx-font-smoothing: grayscale;
+}
+
+.van-icon-success:before {
+	content: "\e626";
+}
+```
+
 ### API
 
 | Attribute | Description | Type | Default | Accepted Values |

docs/markdown/zh-CN/icon.md

@@ -23,6 +23,34 @@ Icon 组件默认引用 `yzcdn.cn` 域名下的字体文件，如果想要使用
 import 'vant/lib/vant-css/icon-local.css';
 ```
 
+#### 自定义字体
+如果我们的Icon数量无法满足你的需求，可以用以下方法，保留原本Icon的情况下，增加更多你想要的Icon
+
+[Demo地址](https://github.com/qianzhaoy/vant--mobile-mall/blob/master/src/assets/scss/iconfont/iconfont.css)
+```css
+@font-face {
+	font-family: "iconfont";
+	src: url('./iconfont.ttf') format('truetype');
+}
+
+@font-face {
+	font-family: "vanIcon";
+	src: url(https://b.yzcdn.cn/zanui/icon/vant-icon-4c3245.ttf) format('truetype');
+}
+
+.van-icon {
+	position: relative;
+	font-family: "iconfont", "vanIcon" !important;
+	font-size: 14px;
+	font-style: normal;
+	-webkit-font-smoothing: antialiased;
+	-moz-osx-font-smoothing: grayscale;
+}
+
+.van-icon-success:before {
+	content: "\e626";
+}
+```
 
 ### API