Package pem implements the PEM data encoding, which originated in Privacy
Enhanced Mail. The most common use of PEM encoding today is in TLS keys and
certificates. See RFC 1421.
Decode will find the next PEM formatted block (certificate, private key
etc) in the input. It returns that block and the remainder of the input. If
no PEM data is found, p is nil and the whole of the input is returned in
rest.