Add note on `-trace` flag
Add note on `-trace` flag

Forgot to add comment in TODO about `-trace`
flag which was only useful for a private build
of `runc`.

Signed-off-by: Phil Estes <dbac1f450dc8326caa7ba104b384a0eca642250c@gmail.com>

estesp/bucketbench,estesp/bucketbench