Update index.md

Author: LiorKogan

content/commands/flushall/index.md

@@ -66,6 +66,7 @@ It is possible to use one of the following modifiers to dictate the flushing mod
 
 * An asynchronous `FLUSHALL` command only deletes keys that were present at the time the command was invoked. Keys created during an asynchronous flush will be unaffected.
 * This command does not delete functions.
+* When using Redis Cluster, this command is identical to `FLUSHDB` since a Redis Cluster supports only database zero.
 
 ## Behavior change history