man: Fix nodelist ring0_addr requirement

corosync.conf(5) said every node must have ring0_addr, but with knet any
ringX_addr works (issue #825). The local node is identified by name,
with ring0_addr only as a fallback.

- Require at least one ringX_addr per node
- Note ring0_addr is required for legacy UDP/UDPU transports
- Recommend name to identify the local node

Signed-off-by: Xin Liang <XLiang@suse.com>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>

man/corosync.conf.5

@@ -812,7 +812,11 @@ directive it is possible to specify specific information about nodes in cluster.
 can contain only
 .B node
 sub-directive, which specifies every node that should be a member of the membership, and where
-non-default options are needed. Every node must have at least ring0_addr field filled.
+non-default options are needed. Every node must have at least one ringX_addr field filled
+(ring0_addr is required for the legacy UDP/UDPU transports). To let corosync identify the
+local node, every node should also have the
+.B name
+option set.
 
 Every node that should be a member of the membership must be specified.