Binaries for the C++ binding file (which includes libbitcoind statically linked in) are distributed for convenience. The binary binding file `bitcoind.node` is published to S3 for later download and installation. Source files can also be built if binaries are not desired.
Ensure you've followed the instructions in the README.md for building the project from source. You will be using node-gyp to build the C++ bindings. A script will then upload the bindings to S3 for later use. You will also need credentials for BitPay's bitcore-node S3 bucket and be listed as an author for the bitcore-node's npm module.