Report the temperature with ESP8266 to MQTT

Blog
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where ( which file or config ) to put
sensor:
platform: mqtt
name: “Temperature”
state_topic: “sensor/temperature”
qos: 0
unit_of_measurement: “ºC”

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configuration.yaml of course.

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I am still fairly new to MQTT. Can someone confirm for me how I would use this sketch if I wanted to connect with multiple ESP MCUs?

Would I just replace ESP8266Client with a unique name for each unit in
if (client.connect("ESP8266Client", mqtt_user, mqtt_password))

Thanks!