You'll need a C compiler (gcc). The recommended way to install Nim is choosenim. On Linux:
$ curl https://nim-lang.org/choosenim/init.sh -sSf | sh
Follow the post-install instructions, and add the nim binary to your PATH.
Get the package
This package is SCM'ed with Fossil. Thus:
Members of the team: ask the mantainer ([email protected]) for the Fossil file, and follow his instructions if you're not familiar with Fossil.
People that want to install a local server: ask the mantainer for the site tarball. This tarball can be uncompressed in a directory and keep going.