docs(wiki): restore <img> tag placeholder in roslibjs tutorial

Author: nevalsar

wiki/tools/__all_subsections.md

@@ -1980,7 +1980,7 @@ You can do more advanced stuff such as subscribing to images, Rviz visualization
 To visualize and update an image stream live within your web app, first you need a placeholder in HTML for your image. Define it as follows within the `body` tag with an unique ID to update it later via JavaScript.
 
 ```
-
+<img id="my_image" style='height: 100%; width: 100%; object-fit: contain' src="/assets/images/placeholder.png">
 ```
 
 Now, you can create a topic handler and subscribe to your image from ROS. Note that, if you want to integrate image streams with `roslibjs`, the ROS socket bridge expects images in compressed format. See this section [here](https://roboticsknowledgebase.com/wiki/tools/stream-rviz/compressing-image-streams) for more details on setting up image compression for your topics.

wiki/tools/roslibjs.md

@@ -145,6 +145,7 @@ You can do more advanced stuff such as subscribing to images, Rviz visualization
 To visualize and update an image stream live within your web app, first you need a placeholder in HTML for your image. Define it as follows within the `body` tag with an unique ID to update it later via JavaScript.
 
 ```
+<img id="my_image" style='height: 100%; width: 100%; object-fit: contain' src="/assets/images/placeholder.png">
 ```
 
 Now, you can create a topic handler and subscribe to your image from ROS. Note that, if you want to integrate image streams with `roslibjs`, the ROS socket bridge expects images in compressed format. See this section [here](https://roboticsknowledgebase.com/wiki/tools/stream-rviz/compressing-image-streams) for more details on setting up image compression for your topics.