Turn the plain Certificate column into a relative markdown link
Source:R/utils_render_register_general.R
adjust_cert_links_relative.Rd`add_cert_links()` leaves `register_table$Certificate` as the plain identifier; this is the one place that turns it into the markdown link `[id](path)` that the md/HTML table rendering needs, using a relative path whose depth depends on the output directory. JSON and CSV exports don't call this function and keep the plain `Certificate ID`/absolute `Certificate Link` columns from `add_cert_links()` instead.