code: func ReadDockerignore(contextDir string) ([]string, error) {
  	var excludes []string
  
  	f, err := os.Open(filepath.Join(contextDir, ".dockerignore"))
  	switch {
  	case os.IsNotExist(err):
  		return excludes, nil
  	case err != nil:
  		return nil, err
  	}
  	defer f.Close()
  
  	return dockerignore.ReadAll(f)
  }
docs: // ReadDockerignore reads the .dockerignore file in the context directory and
  // returns the list of paths to exclude