Review documentation for lifecycle badge placement

[bailliem]

Step 1: review list of experimental functions where API may change.
Step 2: Review documentation of those functions to ensure lifecycle badge is placed in the @description block. See https://cran.r-project.org/web/packages/lifecycle/vignettes/communicate.html
e.g.

#' Add two numbers
#'
#' @description
#' r lifecycle::badge("experimental")
#'
#' This function was deprecated because we realised that it's
#' a special case of the [sum()] function.

Step 3: add experimental back to main package to reflect possible changes to API