additional tweaks for CRAN

[mattsecrest]

1. Linking
   #' Please use one of borrowing_hierarchical_commensurate(), borrowing_none(), or borrowing_full() instead.
   #' Please use one of [borrowing_hierarchical_commensurate()], [borrowing_none()], or [borrowing_full()] instead.

2. Back-ticks
   #' @return data.frame with simulation results.
   #' @return A data.frame with simulation results.

[gravesti]

@mattsecrest Is there something to do here?