docs: fix png extension casing

com.unity.perception/Documentation~/GettingStarted.md

 3. Change the names of the cubes to Cube, Box, and Crate
 4. Position the cubes in front of the Main Camera
 
-![Position of the cubes in front of the Main Camera](images/CompletedScene.png)
+![Position of the cubes in front of the Main Camera](images/CompletedScene.PNG)
 <br/>_Position of the cubes in front of the Main Camera_
 
 5. On each cube, in the Inspector window, add a Labeling component 
-![A labeling component, for example "Crate"](images/LabeledObject.png)
+![A labeling component, for example "Crate"](images/LabeledObject.PNG)
 <br/>_A labeling component, for example "Crate"_
 
 6. Create and set up an IdLabelConfig
    4. In the three label text fields, add the text (Crate, Cube and Box) from the Labeling script on the objects you created in the Scene
 
-![IdLabelConfig with three labels](images/IDLabelingConfigurationFinished.png)
+![IdLabelConfig with three labels](images/IDLabelingConfigurationFinished.PNG)
 <br/>_IdLabelConfig with three labels_
 
 7. Create and set up a SemanticSegmentationLabelingConfiguration
     1. In the Perception Camera script, find the SemanticSegmentationLabeler Camera Labeler. In its Label Config field, select the circle button. 
     2. In the Select SemanticSegmentationLabelConfig window, select the **SemanticSegmentationLabelConfig** you created. 
 
-![Perception Camera Labelers](images/MainCameraLabelConfig.png)
+![Perception Camera Labelers](images/MainCameraLabelConfig.PNG)
 <br/>_Perception Camera Labelers_
 
 
 ![Visualization controls in action](images/controls.gif)
 <br/>_Visualization controls in action_
 
-**Important Note:** The Perception package uses asynchronous processing to ensure reasonable frame rates of a scene. A side effect of real-time visualization is that the labelers must be applied to the capture in its actual frame, which potentially adversely affects the Scene's framerate.
+**Important Note:** The Perception package uses asynchronous processing to ensure reasonable frame rates of a scene. A side effect of real-time visualization is that the labelers must be applied to the capture in its actual frame, which potentially adversely affects the Scene's framerate.