add documentation for ThermoRichardsFlow

...es/process/THERMO_RICHARDS_FLOW/c_THERMO_RICHARDS_FLOW.md

...MO_RICHARDS_FLOW/process_variables/i_process_variables.md

...cess/THERMO_RICHARDS_FLOW/process_variables/t_pressure.md

...s/THERMO_RICHARDS_FLOW/process_variables/t_temperature.md

...ocesses/process/THERMO_RICHARDS_FLOW/t_coupling_scheme.md

.../processes/process/THERMO_RICHARDS_FLOW/t_mass_lumping.md

...s/process/THERMO_RICHARDS_FLOW/t_simplified_elasticity.md

...ses/process/THERMO_RICHARDS_FLOW/t_specific_body_force.md

Documentation/bibliography/other.bib