nitpick: nix flake metadata error is confusing

[OlivierLDff]

Error

Error: 
   0: Getting flake metadata
   1: Parsing `nix flake metadata --json /home/runner/_work/repo/repo/` as JSON
   2: EOF while parsing a value at line 1 column 0

Metadata

key	value
version	0.1.0
os	linux
arch	x86_64

Context

I got this error, because flake.nix is located in a subfolder. nix flake metadata --json report:
path '/home/naostage/dev/repo' does not contain a 'flake.nix', searching up

This is a nitpick to just add a real error to explicitly say flake.nix wasn't found in folder.