Renaming content/NFIRS-5.0 to content/nfirs-5.0 will resolve the problem.
Regarding index.md vs. _index.md, this post might be helpful:
Renaming content/NFIRS-5.0 to content/nfirs-5.0 will resolve the problem.
Regarding index.md vs. _index.md, this post might be helpful: