docs(readme): add why

Author: PatrickJS

README.md

@@ -9,6 +9,13 @@
 # Angular 2 Bootloader
 > Angular 2 Bootloader for async script tag and hmr support
 
+#### Why do I need async tag support?
+Chrome V8 parses script tags with `<script async>` or `<script defer>` on a separate thread once downloading of `index.html` begins. Initial load of your `index.html` improves by up to **10%**
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+![czkf6kfviaamqm6](https://cloud.githubusercontent.com/assets/1016365/21236289/6f7dffd6-c2c8-11e6-97f4-291f8eeeb72d.jpg)
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 ### Install
 > `npm install @angularclass/bootloader --save`