Merge pull request #318 from tznode/topic/updateReadme

Update README

Author: surmon-china

README.md

@@ -173,7 +173,7 @@ Swiper.use({
 ```vue
 <template>
   <swiper :options="swiperOption">
-    <swiper-slide v-for="slide in swiperSlides">I'm Slide {{ slide }}</swiper-slide>
+    <swiper-slide v-for="(slide, index) in swiperSlides" :key="index">I'm Slide {{ slide }}</swiper-slide>
     <div class="swiper-pagination" slot="pagination"></div>
   </swiper>
 </template>