[Usage] For a more concise error log

[hyunsooda]

If an error occurs while executing the walk command, it results in the display of verbose panic logs. Comparatively, the default log output of the GNU ls command appears to be more succinct than that of the walk command. Is it possible to contemplate the adoption of an established convention in the upcoming version?

Concise:

> ls notexist
"notexist": No such file or directory (os error 2)

As-Is:

> lk notexist
panic: open /home/notexist: no such file or directory

goroutine 1 [running]:
main.(*model).list(0xc0000e6000)
	/home/go/pkg/mod/github.com/antonmedv/walk@v1.5.2/main.go:593 +0x2be
main.main()
	/home/go/pkg/mod/github.com/antonmedv/walk@v1.5.2/main.go:101 +0x27b

[antonmedv]

Fixed!