Fix example in crl(1) man page

The default input format is PEM, so explicit "-inform DER" is needed to
read DER-encoded CRL.

CLA: trivial
Reviewed-by: NPaul Yang <yang.yang@baishancloud.com>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7094)

doc/man1/crl.pod

@@ -120,7 +120,7 @@ Convert a CRL file from PEM to DER:
 
 Output the text form of a DER encoded certificate:
 
- openssl crl -in crl.der -text -noout
+ openssl crl -in crl.der -inform DER -text -noout
 
 =head1 BUGS