Added missing codes: KC_MEDIA_FAST_FORWARD and KC_MEDIA_REWIND

Keycodes.md

@@ -116,6 +116,8 @@ The source of truth for these codes is the [keycode.txt](https://github.com/qmk/
 |KC_AUDIO_VOL_DOWN|KC_VOLD||
 |KC_MEDIA_NEXT_TRACK|KC_MNXT||
 |KC_MEDIA_PREV_TRACK|KC_MPRV||
+|KC_MEDIA_FAST_FORWARD|KC_MFFD||
+|KC_MEDIA_REWIND|KC_MRWD||
 |KC_MEDIA_STOP|KC_MSTP||
 |KC_MEDIA_PLAY_PAUSE|KC_MPLY||
 |KC_MEDIA_SELECT|KC_MSEL||