{Documentation} StreamId - Add missing 281-2

Summary:
Add "281-2" StreamId definition
- A GPS signal from the Phone App that is sent only once at the start of the recording.

Reviewed By: PiotrBrzyski

Differential Revision: D66310241

fbshipit-source-id: afcf8049ba1404bc7e9152aecb3e52e58492fc67

website/docs/sensors-measurements.mdx

@@ -75,6 +75,7 @@ Left/Right are relative to the left and right side of the glasses when the user
 |231-1 |Microphones |StereoAudioRecordableClass (231) |1 |`mic0`, `mic1`, `mic2`, ..., `mic6` |getAudioPlayer() |
 |247-1 |Barometer |BarometerRecordableClass (247) |1 |`baro0` |getBarometerPlayer() |
 |281-1 |GPS |GpsRecordableClass (281) |1 | |getGpsPlayer() |
+|281-2 |GPS |GpsRecordableClass (281) |2 | |getGpsPlayer() |
 |283-1 |Bluetooth beacon |BluetoothBeaconRecordableClass (283) |1 | |getBluetoothBeaconPlayer() |
 |285-1 |Time domain |TimeRecordableClass (285) |1 | |getTimeSyncPlayer() |
 |1201-1 |SLAM Camera Left |SlamCameraData (1201) |1 |`camera-slam-left` |getSlamLeftCameraPlayer() |