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Add temperature sensors documentation (#4338)

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# Temperature sensors
It is now possible to measure temperatures with the help of the I²C LM75 and 1-Wire DS18B20 chips. The temperature values can be displayed on the OSD and they are also logged. A total maximum of 8 temperature sensors can be connected.
## LM75
Up to 8 can be connected to the flight controller.
* Package: SOP-8, breakout boards can be found easily
* Interface: I²C
* Supply: 2.7 to 5.5V
* Temperature range: -55 to +125°C
## DS18B20
* Package: TO-92, SO-8, µSOP-8
* Interface: 1-Wire
* Supply: 3.0 to 5.5V (parasitic power not supported)
* Temperature range: -55 to +125°C
None of the flight controllers on the market at the time this documentation is written supports 1-Wire directly. To use these sensors a I²C to 1-Wire interface chip needs to be used, the DS2482. Connect the DS2482 SCL and SDA lines to your FC, add a 4.7kohm pull-up resistor between VCC and the DQ pin then connect all the sensors DQ pin to the DS2482 DQ pin.
## Configuring temperature sensors
The `temp_sensor` CLI command can be used to display and change the temperature sensors configuration. When a new temperature sensor is connected it is automatically detected and will appear in the output of the `temp_sensor` command.
* `temp_sensor` without any argument displays all the sensors configuration
* `temp_sensor reset` deletes all the sensors
* `temp_sensor index type address alarm_min alarm_max label` to configure a new sensor or modify the configuration of an existing one.
### Parameters description
* `index` is the index of the configuration slot you want to change
* `type` can be `1` for LM75 or `2` for DS18B20
* `address` is the address of the device on the bus. 0 to 7 for a LM75 or the full 64bit ROM in hex format for a 18B20
* `alarm_min` the temperature under which the corresponding OSD element will start blinking (decidegrees centigrade)
* `alarm_max` the temperature above which the corresponding OSD element will start blinking (decidegrees centigrade)
* `label` a 4 characters maximum label that is displayed on the OSD next to the temperature value
### Example output
Example output of the `temp_sensor` command on a system with two LM75 and four DS18B20 sensors connected
```
temp_sensor 0 1 0 -200 600
temp_sensor 1 1 1 -200 600
temp_sensor 2 2 7c0118681e1cff28 -200 600
temp_sensor 3 2 7d01186838f2ff28 -200 600
temp_sensor 4 2 210118684001ff28 -200 600
temp_sensor 5 2 f801186750c7ff28 -200 600
temp_sensor 6 0 0 0 0
temp_sensor 7 0 0 0 0
```
To change for example the configuration of the fourth sensor to label `BATT`, minimum value alarm 0.5°C and maximum value alarm 45°C
`temp_sensor 3 2 7d01186838f2ff28 5 450 BATT`