Add docs to pzemac on how to change its address

Most tutorials or suggestions online point to using either the official PZEM tool (windows only) or Tasmota. 
With the suggested snipped it is possible to do it using ESPHome.

components/sensor/pzemac.rst

@@ -83,6 +83,63 @@ Configuration variables:
   the same UART bus. You will need to set the address of each device manually. Defaults to ``1``.
 - **modbus_id** (*Optional*, :ref:`config-id`): Manually specify the ID of the Modbus hub.
 
+
+Changing the address of a PZEM-004T:
+------------------------
+
+You can use the following configuration to change the address of a sensor.
+You must set the ``address`` of the ``modbus_controller`` to the current address, and ``new_address`` of the ``on_boot`` lambda to the new one.
+
+.. warning::
+
+    This should be used only once! After changing the address, this code should be removed from the ESP before using the actual sensor code.
+    
+.. code-block:: yaml
+
+    esphome:
+      ...
+      on_boot:
+        ## configure controller settings at setup
+        ## make sure priority is lower than setup_priority of modbus_controller
+        priority: -100
+        then:
+          - lambda: |-
+              auto new_address = 0x03;
+
+              if(new_address < 0x01 || new_address > 0xF7) // sanity check
+              {
+                ESP_LOGE("ModbusLambda", "Address needs to be between 0x01 and 0xF7");
+                return;
+              }
+
+              esphome::modbus_controller::ModbusController *controller = id(epever);
+              auto set_addr_cmd = esphome::modbus_controller::ModbusCommandItem::create_write_single_command(
+                controller, 0x0002, new_address);
+
+              delay(200) ;
+              controller->queue_command(set_addr_cmd);
+              ESP_LOGI("ModbusLambda", "PZEM Addr set");
+
+    modbus:
+      send_wait_time: 200ms
+      id: mod_bus_epever
+
+    modbus_controller:
+      - id: epever
+        ## the current device addr
+        address: 0x1
+        modbus_id: mod_bus_epever
+        command_throttle: 0ms
+        setup_priority: -10
+        update_interval: 30s
+
+    uart:
+      rx_pin: GPIO16
+      tx_pin: GPIO17
+      baud_rate: 9600
+      stop_bits: 2
+
+
 See Also
 --------