The recommended method for installing assetrinc is via Composer. If you are not familiar with Composer, check out the Composer documentation.
Assetrinc's package name is assetrinc/assetrinc.
It is highly recommended that you require a specific version of assetrinc in your composer.json for now. That is, do not include 0.0.* or ~0.0.6, but instead include 0.0.6. Assetrinc is still undergoing research and development, so backwards incompatible changes are still likely to occur between versions.