[DOCS] Wrong data type for VS rate

[DocMoebiuz]

The docs state that all display values are sent as 2 byte UInt16.

But for V/S we actually want to use Int16 so that we can display negative values.

Current docs:

| V/S Number | High 8 bit of Uint16 | - | 21 | - | 0x00 |
| V/S Number | Low 8 bit of Uint16 | - | 22 | - | 0x00 |

Should:

| V/S Number | High 8 bit of Int16 | - | 21 | - | 0x00 |
| V/S Number | Low 8 bit of Int16 | - | 22 | - | 0x00 |

[DocMoebiuz]

Issue reported by user
MobiFlight/MobiFlight-Connector#2490

Pull request with fix
MobiFlight/MobiFlight-Connector#2526