Clarify dashes are required for openssl list command

Fixes #19013

CLA: trivial

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from #19031)

doc/man1/openssl.pod

@@ -13,13 +13,13 @@ I<command>
 
 B<openssl>
 B<list>
-B<standard-commands> |
-B<digest-commands> |
-B<cipher-commands> |
-B<cipher-algorithms> |
-B<digest-algorithms> |
-B<mac-algorithms> |
-B<public-key-algorithms>
+B<-standard-commands> |
+B<-digest-commands> |
+B<-cipher-commands> |
+B<-cipher-algorithms> |
+B<-digest-algorithms> |
+B<-mac-algorithms> |
+B<-public-key-algorithms>
 
 B<openssl> B<no->I<XXX> [ I<options> ]