highlight performance impact of lock tracing

[duncdrum]

and means of disabling lock table logging (hint for production best practices)

Where is the problem

As discussed during community call on 19/08/19 regarding performance of 5.0.0

What is the problem

Users should know that turning this off makes things go faster, and how to trun it off.

See #333

Please provide the following

• exist-db version: 5.0.0
• documentation version: 5.0.0-RC3