Add reset_reason text sensor to debug component (#2302)

components/debug.rst

@@ -25,6 +25,8 @@ ESP heap memory (free space, maximum free block size and fragmentation level) an
       - platform: debug
         device:
           name: "Device Info"
+        reset_reason:
+          name: "Reset Reason"
 
     sensor:
       - platform: debug
@@ -70,6 +72,13 @@ Configuration variables:
   - **name** (**Required**, string): The name of the sensor.
   - All other options from :ref:`Text Sensor <config-text_sensor>`.
 
+- **reset_reason** (*Optional*): Reports the last reboot reason in a human-readable form.
+
+  Accepts these options:
+
+  - **name** (**Required**, string): The name of the sensor.
+  - All other options from :ref:`Text Sensor <config-text_sensor>`.
+
 Sensor
 -------
 Configuration variables: