keypad: add doc that reset() can be used to determine keys held down …

…at startup

shared-bindings/keypad/KeyMatrix.c

@@ -159,6 +159,9 @@ static void check_for_deinit(keypad_keymatrix_obj_t *self) {
 //|         """Reset the internal state of the scanner to assume that all keys are now released.
 //|         Any key that is already pressed at the time of this call will therefore immediately cause
 //|         a new key-pressed event to occur.
+//|         For instance, if you call `reset()` immediately after creating a `KeyMatrix` object
+//|         at the beginning of your program, the events it generates will let you determine which keys
+//|         were being held down at program start.
 //|         """
 //|         ...
 

shared-bindings/keypad/Keys.c

@@ -147,6 +147,9 @@ static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(keypad_keys___exit___obj, 4, 4, keypa
 //|         """Reset the internal state of the scanner to assume that all keys are now released.
 //|         Any key that is already pressed at the time of this call will therefore immediately cause
 //|         a new key-pressed event to occur.
+//|         For instance, if you call `reset()` immediately after creating a `Keys` object
+//|         at the beginning of your program, the events it generates will let you determine which keys
+//|         were being held down at program start.
 //|         """
 //|         ...
 

shared-bindings/keypad/ShiftRegisterKeys.c

@@ -201,6 +201,9 @@ static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(keypad_shiftregisterkeys___exit___obj
 //|         """Reset the internal state of the scanner to assume that all keys are now released.
 //|         Any key that is already pressed at the time of this call will therefore immediately cause
 //|         a new key-pressed event to occur.
+//|         For instance, if you call `reset()` immediately after creating a `ShiftRegisterKeys` object
+//|         at the beginning of your program, the events it generates will let you determine which keys
+//|         were being held down at program start.
 //|         """
 //|         ...
 

shared-bindings/keypad_demux/DemuxKeyMatrix.c

@@ -147,6 +147,9 @@ static void check_for_deinit(keypad_demux_demuxkeymatrix_obj_t *self) {
 //|         """Reset the internal state of the scanner to assume that all keys are now released.
 //|         Any key that is already pressed at the time of this call will therefore immediately cause
 //|         a new key-pressed event to occur.
+//|         For instance, if you call `reset()` immediately after creating a `DemuxKeyMatrix` object
+//|         at the beginning of your program, the events it generates will let you determine which keys
+//|         were being held down at program start.
 //|         """
 //|         ...