update angular comparison (close #178)

Author: yyx990803

src/guide/comparison.md

@@ -12,11 +12,13 @@ There are a few reasons to use Vue over Angular, although they might not apply f
 
 - Vue.js is a more flexible, less opinionated solution. That allows you to structure your app the way you want it to be, instead of being forced to do everything the Angular way. It's only an interface layer so you can use it as a light feature in pages instead of a full blown SPA. It gives you bigger room to mix and match with other libraries, but you are also responsible for making more architectural decisions. For example, Vue.js' core doesn't come with routing or ajax functionalities by default, and usually assumes you are building the application using an external module bundler. This is probably the most important distinction.
 
-- Vue.js has better performance and is much, much easier to optimize, because it doesn't use dirty checking. Angular gets slow when there are a lot of watchers, because every time anything in the scope changes, all these watchers need to be re-evaluated again. Also, the digest cycle may have to run multiple times to "stabilize" if some watcher triggers another update. Angular users often have to resort to esoteric techniques to get around the digest cycle, and in some situations there's simply no way to optimize a scope with a large amount of watchers. Vue.js doesn't suffer from this at all because it uses a transparent dependency-tracking observing system with async queueing - all changes trigger independently unless they have explicit dependency relationships. The only optimization hint you'll ever need is the `track-by` param on `v-for` lists.
+- Angular uses two-way binding between scopes. While Vue also supports explicit two-way bindings, it defaults to a one-way, parent-to-child data flow between components. Using one-way binding makes the flow of data easier to reason about in large apps.
 
 - Vue.js has a clearer separation between directives and components. Directives are meant to encapsulate DOM manipulations only, while Components stand for a self-contained unit that has its own view and data logic. In Angular there's a lot of confusion between the two.
 
-Interestingly, quite a few Angular 1 issues that are non-existent in Vue are also addressed by the design decisions in Angular 2.
+- Vue.js has better performance and is much, much easier to optimize, because it doesn't use dirty checking. Angular gets slow when there are a lot of watchers, because every time anything in the scope changes, all these watchers need to be re-evaluated again. Also, the digest cycle may have to run multiple times to "stabilize" if some watcher triggers another update. Angular users often have to resort to esoteric techniques to get around the digest cycle, and in some situations there's simply no way to optimize a scope with a large amount of watchers. Vue.js doesn't suffer from this at all because it uses a transparent dependency-tracking observing system with async queueing - all changes trigger independently unless they have explicit dependency relationships. The only optimization hint you'll ever need is the `track-by` param on `v-for` lists.
+
+Interestingly, there are quite some similarities in how Angular 2 and Vue are addressing these Angular 1 issues.
 
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