connect approaches to code in metab_Kmodel help file

These are being left out to dry right now:

``` r
#' \itemize{
#'
#' \item{"mean"}{Predict K as the mean of all K values}
#'
#' \item{"weighted mean"}{Predict K as the mean of all K values, weighted by the
#' inverse of the confidence intervals in the input K values}
#'
#' \item{"KvQ"}{Regress K versus Q, tending toward overall mean in ranges of Q
#' with sparse data}
#'
#' \item{"weighted KvQ"}{Regress K versus Q, tending toward overall mean in
#' ranges of Q with sparse data, weighting high-confidence K values more
#' heavily}
#'
#' \item{"T smoother"}{Predict K using a loess or spline smoother over time}
#'
#' \item{"Q smoother"}{Predict K using a loess or spline smoother over
#' discharge.daily}
#'
#' \item{"TQ smoother"}{Predict K using a loess or spline smoother over both
#' time and discharge.daily}
#'
#' }
```