docs: update delaytop documentation for new interactive features

This commit updates the delaytop documentation to reflect the newly
added features:
1) Added comprehensive description of interactive keyboard controls
2) Documented all available sort fields
3) Added examples for advanced usage scenarios
4) Included PSI availability note

Link: https://lkml.kernel.org/r/20250907001457696qAqUGGkV1VfEO6OkVMovW@zte.com.cn


Signed-off-by: Fan Yu <fan.yu9@zte.com.cn>
Reviewed-by: xu xin <xu.xin16@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>