PM1006: add note regarding standalone UART init (#3240)

* add note regarding standalone init

* Update pm1006.rst

components/sensor/pm1006.rst

@@ -69,6 +69,22 @@ Example config:
           name: "Particulate Matter 2.5µm Concentration"
         update_interval: 20s
 
+
+If you run the PM1006 (2.5µm) or PM1006K (1, 2.5, 10µm) independent from the original MCU you need to send a serial command in the first 5 seconds after power is applied to the sensor. Otherwise the sensor will switch to PWM mode and does not repond to UART requests. A possibility to do this in ESPhome is to use an automation. `Source <https://community.home-assistant.io/t/ikea-vindriktning-air-quality-sensor/324599/300>`_
+
+Example config:
+
+.. code-block:: yaml
+
+    # Example configuration entry
+    on_boot:
+      priority: 240
+      then:
+        - uart.write:
+            id: ikea #id of the uart bus used for the PM1006
+            data: [0x11, 0x02, 0x0B, 0x01, 0xE1]
+
+
 See Also
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