update index.md with Chinese simplified links

[alaskasquirrel]

[vindarel]

nice to see those resources.

It might be more readable to put those links on a newline as a sub-bullet, wouldn't it?

* [Practical Common Lisp](http://www.gigamonkeys.com/book/) by Peter Seibel
  *  [Chinese simplified](https://binghe.github.io/pcl-cn/).

or

* [Practical Common Lisp](http://www.gigamonkeys.com/book/) by Peter Seibel
  *  [PCL (Chinese simplified)](https://binghe.github.io/pcl-cn/).

[alaskasquirrel]

as a sub-bullet, look ok.

[alaskasquirrel]

may be add: A Road to Common Lisp Steve Losh, Chinese simplified.