[dallas_temp] Add index parameter (#5500)

Author: leejoow

content/components/sensor/dallas_temp.md

@@ -14,17 +14,27 @@ and similar 1-Wire temperature sensors. A {{< docref "/components/one_wire/index
 required to be set up in your configuration for this sensor to work.
 
 ```yaml
-# Example configuration entry
+# Example configuration entries
 sensor:
+  # only one device
   - platform: dallas_temp
-    address: 0x1234567812345628
     name: temperature
     update_interval: 120s
+  # specific address
+  - platform: dallas_temp
+    address: 0x1234567812345628
+    name: temperature2
+  # second device
+  - platform: dallas_temp
+    index: 1
+    name: temperature1
 ```
 
 ## Configuration variables
 
-- **address** (*Optional*, int): The address of the sensor. Required if there is more than one device on the bus.
+- **address** (*Optional*, int): The address of the sensor. Required if there is more than one device on the bus and index is not specified.
+- **index** (*Optional*, byte): The index (0-based) of the sensor. Required if there is more than one device on the bus and address is not specified.
+  *Note this index is based on the hardware addresses of the sensors and the order can change if sensors are changed, added, or removed.*
 - **resolution** (*Optional*, int): An optional resolution from 9 to 12. Higher means more accurate.
   Defaults to the maximum for most Dallas temperature sensors: 12.