doorlock: document different doorlock images for each lock variant

We now have different images for each doorlock variant. Documenting 
this in the build and flash instructions.

Relate-to: eclipse/oniro-blueprints/oniro-blueprints-docs/docs#2



Signed-off-by: Francesco Pham <francesco.pham@huawei.com>

doorlock.rst

@@ -269,7 +269,19 @@ Build the software
 
 
 #. 
-    Start building the image
+    There are different images that you can build, depending on the lock variant 
+    you want to operate:
+
+    * The **zephyr-blueprint-doorlock** image is used primarily for testing. It 
+      is not an actual lock but just a doorlock simulated on the board's LED 
+      light, turning on/off the light when the lock is locked/unlocked. 
+    * The **zephyr-blueprint-dootlock-solenoid** image is for the lock variant 
+      using the lock-style solenoid.
+    * The **zephyr-blueprint-doorlock-rotating** image is for the lock variant
+      using the rotating motor.
+    
+    Start building the image with the following command, replacing 
+    `zephyr-blueprint-doorlock` with the image name of your choice.
 
     .. code-block:: bash
 
@@ -282,7 +294,9 @@ Flash the software when built with bitbake
     port to your computer and putting the board into flashing mode by 
     double-pressing the reset button.
 #. 
-    Flash the door lock software to the board:
+    Flash the door lock software to the board with the following command, 
+    replacing `zephyr-blueprint-doorlock` with the name of the image that you 
+    built in the previous step.
 
     .. code-block:: bash
 
@@ -302,6 +316,17 @@ Alternative way of building the software (using west)
         $ west init --mr v2.7.0
         $ west update
         $ git clone https://gitlab.eclipse.org/eclipse/oniro-blueprints/doorlock/doorlock-zephyr.git
+
+#.
+    By default only the LED variant of the doorlock is enabled, which simulates 
+    the lock using the board's LED light. Modify the `doorlock-zephyr/prj.conf` 
+    file to enable the doorlock variant of your choice. 
+
+#.
+    Start building the image:
+
+    .. code-block:: bash
+
         $ west build -p auto -b arduino_nano_33_ble doorlock-zephyr
 
 Flashing the software when built with west