Prezto is a configuration framework for zsh aimed at providing better defaults and other conveniences. However, to avoid feature bloat in the core repository, prezto-contrib was born. This repository is meant to include additional modules which are either not ready for inclusion in prezto-core or don't currently have a maintainer willing to support them.
Multiple module directory support is built into prezto, so it's pretty easy to use these modules. Simply do the following:
cd $ZPREZTODIR
git clone --recurse-submodules https://github.com/belak/prezto-contrib contrib
After the repo is cloned, you can load modules in the same way you'd load a normal prezto module.
Alternatively, you can clone contrib elsewhere and update the module dirs setting.