Potential issue with <readme> shortcode

[SteveClement]

Currently to generate the short code in content files we simply do the following in layouts/shortcodes/readme.html:

{{ $data := resources.GetRemote ( printf "https://raw.githubusercontent.com/%s/master/README.md"  $.Page.Params.repository) }}
{{ $data.Content | markdownify | safeHTML }}

This hard codes the 'master' branch and can result in potential broken build if only 'main' or another default branch exist.
Currently, even if master does not exist, it will server the main branch, e.g: https://raw.githubusercontent.com/range42/range42/master/README.md
This behaviour might change in the future.

Better would be:

{{ $repo := $.Page.Params.repository }}
{{ $main := resources.GetRemote (printf "https://raw.githubusercontent.com/%s/main/README.md" $repo) }}
{{ with $main }}
  {{ .Content | markdownify | safeHTML }}
{{ else }}
  {{ $master := resources.GetRemote (printf "https://raw.githubusercontent.com/%s/master/README.md" $repo) }}
  {{ with $master }}
    {{ .Content | markdownify | safeHTML }}
  {{ else }}
    {{ warnf "readme shortcode: README.md not found on main or master for repository %s" $repo }}
    <p><em>README.md not found for {{ $repo }}.</em></p>
  {{ end }}
{{ end }}