Retain additional steady-state parameters

The new parameters rho_slope and rho_infection are also required.

vignettes/rbc-steady-state.Rmd

@@ -40,7 +40,7 @@ Note that only a subset of the model parameters are required to calculate the RB
 ```{r subset}
 only_params <- c(
   "T_urbc", "T_R", "T_M", "T_n",
-  "T_R_min", "kappa", "rho0",
+  "T_R_min", "kappa", "rho0", "rho_slope", "rho_inflection",
   "U_ss", "R_a_ss", "N_a_ss",
   "lambdaU.sel",
   "M_t_1",