Update components.md (vuejs#611)

Alex Lee · chrisvfritz · commit 6f513a9ad18a · 2016-11-26T23:43:59.000-05:00
Makes more sense and easy to understand.
diff --git a/src/v2/guide/components.md b/src/v2/guide/components.md
@@ -549,7 +549,7 @@ is just syntactic sugar for:
 When used with a component, this simplifies to:
 
 ``` html
-<input v-bind:value="something" v-on:input="something = arguments[0]">
+<custom-input v-bind:value="something" v-on:input="something = arguments[0]"></custom-input>
 ```
 
 So for a component to work with `v-model`, it must:
