Address runtime performance in user guide

[forman]

Is your feature request related to a problem? Please describe.

Users and developers should know where runtime performance bottlenecks may originate from and should learn how to setup their environment and configuration for best zappend performance.

Describe the solution you'd like

• Make basic performance analysis to have some stats that demonstrate impact of filesystem and turning transaction management on and off, and potentially other configuration settings,
• Write section in user guide that provides tips for best performance and describes zappend features that help analyse performance bottlenecks, i.e., logging + profiling. Include the stats from above. List configuration parameters that have impact on performance.
• Optional: simplify logging (see Simplify configuration for logging to console #65) and profiling configuration or adjust defaults to ease performance analysis.

See #34.
See #35.