[intra_process_demo] executable name in README.md fix-up (#690)

Signed-off-by: Trushant Adeshara <[email protected]>
(cherry picked from commit 4a18995)

intra_process_demo/README.md

@@ -72,10 +72,10 @@ This starts the `camera_node` ROS 2 node and publishes images captured from your
 ros2 run intra_process_demo camera_node
 ```
 
-This starts the `watermarked_node` ROS 2 node which subscribes to raw images from ROS 2 topic `/image`, overlays both **process ID number** and **message address** on top of the image visually and publishes to ROS 2 topic `/watermarked_image`.
+This starts the `watermark_node` ROS 2 node which subscribes to raw images from ROS 2 topic `/image`, overlays both **process ID number** and **message address** on top of the image visually and publishes to ROS 2 topic `/watermarked_image`.
 ```bash
 # Open new terminal
-ros2 run intra_process_demo watermarked_node
+ros2 run intra_process_demo watermark_node
 ```
 
 This starts the `image_view_node` ROS 2 node which subscribes to `/watermarked_image` and displays the received images in an OpenCV GUI window.