[#1593] node/config_example: Add description of morph/cache_ttl=0 behavior

Signed-off-by: Alexander Chuprov <a.chuprov@yadro.com>

config/example/node.yaml

@@ -79,7 +79,8 @@ contracts:  # side chain NEOFS contract script hashes; optional, override values
 
 morph:
   dial_timeout: 30s  # timeout for side chain NEO RPC client connection
-  cache_ttl: 15s  # Sidechain cache TTL value (min interval between similar calls). Negative value disables caching.
+  cache_ttl: 15s  # Sidechain cache TTL value (min interval between similar calls).
+                  # Negative value disables caching. A zero value sets the default value.
                   # Default value: block time. It is recommended to have this value less or equal to block time.
                   # Cached entities: containers, container lists, eACL tables.
   container_cache_size: 100 # container_cache_size is is the maximum number of containers in the cache.