Add link to libilbc project on iLBC page

[TimothyGu]

Hi, I'm the maintainer of the libilbc library, which essentially extracts out the parts of WebRTC needed to support a standalone iLBC codec. It's used by FFmpeg and is packaged by Homebrew, Arch Linux, Gentoo, and a few other Linux distros. It would be nice if you could include a link to the project on the webpage. (I understand that this repo is deprecated, but this page seems to be the only official Google reference to iLBC.) Thanks!