xbzrle: update xbzrle doc

Add new parameter description, also:
1. Remove unsociable space.
2. Nit picking: s/two/2 in report

Signed-off-by: Mao Zhongyi <maozhongyi@cmss.chinamobile.com>
Message-Id: <20200320143216.423374-1-maozhongyi@cmss.chinamobile.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>