Keep track of processes killed in the termshark log file

Some larger loader changes are coming to address some intermittent bugs
I found while jumping around pcaps using packet marks.

pcap/cmds_unix.go

@@ -10,6 +10,7 @@ import (
 	"syscall"
 
 	"github.com/pkg/errors"
+	log "github.com/sirupsen/logrus"
 )
 
 func (c *Command) PutInNewGroupOnUnix() {
@@ -25,5 +26,6 @@ func (c *Command) Kill() error {
 	if c.Cmd.Process == nil {
 		return errors.WithStack(ProcessNotStarted{Command: c.Cmd})
 	}
+	log.Infof("Sending SIGTERM to %v: %v", c.Cmd.Process.Pid, c.Cmd)
 	return syscall.Kill(-c.Cmd.Process.Pid, syscall.SIGTERM)
 }