make explanation more clear, thank @daniel!

Author: HerringtonDarkholme

src/v2/guide/typescript.md

@@ -142,8 +142,8 @@ var vm = new Vue({
 
 ## Annotating Return Type
 
-Vue's type definition is prone to [circular reference](https://github.com/Microsoft/TypeScript/issues/12846#issuecomment-270296195) of `this`.
-Annotating return type is highly recommended to avoid such error.
+Because of the circular nature of Vue's declaration files, TypeScript may have difficulties inferring the types of certain methods.
+For this reason, you may need to annotate the return type on methods like `render` and those in `computed`.
 
 ```ts
 import Vue, { VNode } from 'vue'
@@ -173,4 +173,5 @@ const Component = Vue.extend({
 })
 ```
 
-If you find type inference or member completion doesn't work, you can try annotating method return type.
+If you find type inference or member completion isn't working, annotating certain methods may help address these problems.
+Using the `--noImplicitAny` option will help find many of these unannotated methods.