docs: update code demo and code annotation (#931)

Author: brenner8023

README.md

@@ -347,7 +347,7 @@ export default {
 > Similarly, in Vue 2 you will need to call `del` to [ensure a key deletion triggers view updates](https://vuejs.org/v2/api/#Vue-delete) in reactive objects (similar to `Vue.delete` but for `reactive objects` created by the Composition API). In Vue 3 you can just delete them by calling `delete foo.bar`.
 
 ```ts
-import { reactive, set } from '@vue/composition-api'
+import { reactive, set, del } from '@vue/composition-api'
 
 const a = reactive({
   foo: 1

README.zh-CN.md

@@ -187,7 +187,7 @@ b.list[1].count === 1 // true
 > ⚠️ 警告: `set` 和 `del` 并非 Vue 3 的一部分。由于 [Vue 2.x 响应式系统的限制](https://vuejs.org/v2/guide/reactivity.html#For-Objects)，我们在插件中提供该 API 作为添加响应式属性的一个变通方案。在 Vue 3 中，你只需要直接为属性赋值即可。
 
 ```ts
-import { reactive, set } from '@vue/composition-api'
+import { reactive, set, del } from '@vue/composition-api'
 
 const a = reactive({
   foo: 1

src/apis/effectScope.ts

@@ -84,7 +84,7 @@ export function recordEffectScope(
     scope.effects.push(effect)
     return
   }
-  // destory on parent component unmounted
+  // destroy on parent component unmounted
   const vm = getCurrentInstance()?.proxy
   vm && vm.$on('hook:destroyed', () => effect.stop())
 }
@@ -103,7 +103,7 @@ export function onScopeDispose(fn: () => void) {
   } else if (__DEV__) {
     warn(
       `onScopeDispose() is called when there is no active effect scope` +
-        ` to be associated with.`
+      ` to be associated with.`
     )
   }
 }