Update/remove dead links to the LiL paper in README.

[pranavats]

The following links mentioned in the README seem to be dead (404 errors)

https://common-lisp.net/~frideau/lil-ilc2012/lil-ilc2012.pdf
https://common-lisp.net/~frideau/lil-ilc2012/lil-ilc2012.html

[fare]

The hosting of common-lisp.net has changed. I see no equivalent for ~frideau, though. I may have to look for an alternative hosting solution...