docs: link-ify vignette("backtesting", package="epipredict")

`downlit` fails to link these, maybe because we're not on CRAN yet.

Author: brookslogan

R/methods-epi_archive.R

@@ -629,7 +629,8 @@ epix_detailed_restricted_mutate <- function(.data, ...) {
 #' version-aware: the sliding computation at any given reference time t is
 #' performed on **data that would have been available as of t**. This function
 #' is intended for use in accurate backtesting of models; see
-#' `vignette("backtesting", package="epipredict")` for a walkthrough.
+#' \href{https://cmu-delphi.github.io/epipredict/articles/backtesting.html}{`vignette("backtesting",
+#' package="epipredict")`} for a walkthrough.
 #'
 #' @param .x An [`epi_archive`] or [`grouped_epi_archive`] object. If ungrouped,
 #'   all data in `x` will be treated as part of a single data group.

man/epix_slide.Rd

@@ -234,7 +234,8 @@ observation carried forward (LOCF). For more information, see `epix_merge()`.
 ## Backtesting forecasting models
 
 One of the most common use cases of `epiprocess::epi_archive()` object is for
-accurate model backtesting. See `vignette("backtesting", package="epipredict")`
+accurate model backtesting. See [`vignette("backtesting",
+package="epipredict")`](https://cmu-delphi.github.io/epipredict/articles/backtesting.html)
 for an in-depth demo, using a pre-built forecaster in that package.
 
 ## Attribution