Fix MANIFEST.SKIP or use an authoring tool which respects MANIFEST.SKIP. Note that each entry in MANIFEST.SKIP is a regular expression. You may need to add appropriate meta characters not to ignore necessary stuff.
Add all modules contained in this distribution to the META.yml field 'provides'. Module::Build or Dist::Zilla::Plugin::MetaProvides do this automatically for you.
This is not a critical issue. Currently mainly informative for the CPANTS authors. It might be removed later.