Add more explanation and examples for logbackBatchingSettings

[blakeli0]

Below is an example configuration for logbackBatchingSettings in the usage section in README.

<logbackBatchingSettings>
      <elementCountThreshold>100</elementCountThreshold>
      <requestByteThreshold>1000</requestByteThreshold>
      <delayThreshold>500</delayThreshold>
      <maxOutstandingElementCount>10000</maxOutstandingElementCount>
      <maxOutstandingRequestBytes>100000</maxOutstandingRequestBytes>
      <limitExceededBehavior>Ignore</limitExceededBehavior>
</logbackBatchingSettings> 

There are very little information regarding what exactly does each configuration mean, what are the possible problems if they are not properly configured and how to tweak them to improve the performance. Hence customers are usually staying with the defaults that are not optimized for high throughput scenarios.