Default value for state.dir is confusing

The default value for state.dir is documented as /var/folders/0t/68svdzmx1sld0mxjl8dgmmzm0000gq/T//kafka-streams

This is misleading, the value will be different in each environment as it computed using System.getProperty("java.io.tmpdir"). We should update the description to mention how the path is computed.