doc: Added section on log rotation.

fixes: #3776

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Added hyperlink to log rotation section.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Added link to rotation section.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>