Doc: Improve CPU Usage Analyzer documentation

Add sections about extra command line options and troubleshooting.

Change-Id: I2ecd7b32a211321bcf9c31ee65f92386b70958db
Reviewed-by: Kari Hautamäki <kari.hautamaki@theqtcompany.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>