Provide explanation of ConcludesBatch Event Handler parameter

[smcvb]

The @ConcludesBatch can be used in @EventHandler annotated function to check whether a batch of events has concluded yes/no.
This is beneficial in situations where optimization of a query model update are required to only occur after a batch of events has been rounded up.

This thus translates to a short explanation in the 'performance tuning' section to describe this functionality.