add comment, on ford stock long, prchg seems to be set from the possible future accel

selfdrive/car/ford/fordcan.py

@@ -117,6 +117,7 @@ def create_acc_msg(packer, long_active: bool, gas: float, accel: float, stopping
     "Cmbb_B_Enbl": 1 if long_active else 0,           # Enabled: 0=No, 1=Yes
     "AccPrpl_A_Rq": gas,                              # Acceleration request: [-5|5.23] m/s^2
     "AccResumEnbl_B_Rq": 1 if long_active else 0,
+    # TODO: we may be able to improve braking response by utilizing pre-charging
     "AccBrkPrchg_B_Rq": decel,                        # Pre-charge brake request: 0=No, 1=Yes
     "AccBrkDecel_B_Rq": decel,                        # Deceleration request: 0=Inactive, 1=Active
     "AccStopStat_B_Rq": 1 if stopping else 0,