[guide] [es5] Remove ES5 guide and mark it deprecated.

Fixes airbnb#941.

Author: ljharb

Diff for: README.md

@@ -7,7 +7,7 @@
 [![Gitter](https://badges.gitter.im/Join Chat.svg)](https://gitter.im/airbnb/javascript?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
 
 Other Style Guides
- - [ES5](es5/)
+ - [ES5 (Deprecated)](https://github.com/airbnb/javascript/tree/es5-deprecated/es5)
  - [React](react/)
  - [CSS & Sass](https://github.com/airbnb/css)
  - [Ruby](https://github.com/airbnb/ruby)