Improve information about risks for forceSync config option

https://zookeeper.apache.org/doc/r3.5.5/zookeeperAdmin.html#Unsafe+Options

The following options can be useful, but be careful when you use them. The risk of each is explained along with the explanation of what the variable does.

forceSync : (Java system property: zookeeper.forceSync) Requires updates to be synced to media of the transaction log before finishing processing the update. If this option is set to no, ZooKeeper will not require updates to be synced to the media.

The risks for this option are not very clear. Does it only the risk of loss some recent committed transactions if all Zookeeper instances from an ensemble are crashed and restarted at almost the same time or some other problems are also possible?