code: func makeCertificateFromDisk(certFile, keyFile string) (Certificate, error) {
  	certPEMBlock, err := ioutil.ReadFile(certFile)
  	if err != nil {
  		return Certificate{}, err
  	}
  	keyPEMBlock, err := ioutil.ReadFile(keyFile)
  	if err != nil {
  		return Certificate{}, err
  	}
  	return makeCertificate(certPEMBlock, keyPEMBlock)
  }
docs: // makeCertificateFromDisk makes a Certificate by loading the
  // certificate and key files. It fills out all the fields in
  // the certificate except for the Managed and OnDemand flags.
  // (It is up to the caller to set those.)