Add recipe: soundcloud

Hello! I am the author of the `soundcloud` package, which can be found [here](https://github.com/tthieman/soundcloud.el).

This package allows the user to find artists on SoundCloud and play tracks from them. `deferred` is used to communicate with the SoundCloud API, and music is played using `EMMS`. The package also requires `mplayer` to be installed on the system. I'd appreciate any instructions on how to properly handle letting the user know about that within Emacs itself, but the installation blurb on my GitHub page has some installation instructions.