edgeHub 1.1.5: UsePooledBuffers is undocumented

## Expected Behavior

The `UsePooledBuffers` should be documented somewhere, for instance https://docs.microsoft.com/en-us/azure/iot-edge/production-checklist?view=iotedge-2018-06&preserve-view=true

## Current Behavior

`UsePooledBuffers` documentation is nowhere to be found. The production-readyness document at https://docs.microsoft.com/en-us/azure/iot-edge/production-checklist?view=iotedge-2018-06&preserve-view=true explains to set `OptimizeForPerformance` to false on constrained devices to disable the `PooledByteBufferAllocator` along with reduced memory requirement of `RocksDb`, but since 1.1.5 with commit https://github.com/Azure/iotedge/commit/50027ff39e22e45335c5ce5f30e0fda23d8f26be the undocumented flag `UsePooledBuffers` has been split out, making `OptimizeForPerformance` not switch them off, yet this flag is nowhere documented and also not referenced in the aforementioned document.

This leads to an uncertainty amongst users of "constrained" IoT devices if they can safely upgrade to 1.1.5

### Runtime Versions

edgeHub 1.1.5