instruction: Write Go code to go by example: directories
output: ```dockerfile
  $ go run directories.go
  Listing subdir/parent
   child true
   file2 false
   file3 false
  Listing subdir/parent/child
   file4 false
  Visiting subdir
   subdir true
   subdir/file1 false
   subdir/parent true
   subdir/parent/child true
   subdir/parent/child/file4 false
   subdir/parent/file2 false
   subdir/parent/file3 false
  ```