See the installation and other documentation in the PDF manual. A changelog is also available.
The cannonical reference for RH is Uitenbroek, H. 2001, ApJ, 557, 389 (ADS: 2001ApJ...557..389U, DOI: 10.1086/321659).
han-uitenbroek/RH
Radiative transfer code based on the multi-level approximate lambda iteration formalism of Rybicki & Hummer (1991, 1992). The code solves the combined equations of statistical equilibrium and radiative transfer for multi-level atoms and molecules in a given plasma under general Non-LTE conditions.
C