code: func (a Afero) ReadFile(filename string) ([]byte, error) {
  	return ReadFile(a.Fs, filename)
  }
docs: // ReadFile reads the file named by filename and returns the contents.
  // A successful call returns err == nil, not err == EOF. Because ReadFile
  // reads the whole file, it does not treat an EOF from Read as an error
  // to be reported.