I dunno why to install it actually.

Building dependencies on debian-based systems:
libfreetype6-dev libopenal-dev libsdl2-dev libpng12-dev libjpeg62-turbo-dev libvorbis-dev libogg-dev

If you are using another Linux distribution, install the corresponding packages.
After that a simple 'make' should do the work for you. If it doesn't, you have to modify it manually...

(Important) For Windows users:
PLEASE DO NOT BUILD THE CURRENT VERSION!!!
SMELT now only supports OpenGL. It works on Windows indeed but very inefficiently...