fix: link to image (#31454)

windows progress bar image was linked with square brackets [] insted of parenthesis () and to github asset storage instead of local image directory.

docs/tutorial/progress-bar.md

@@ -7,7 +7,7 @@ without the need of switching to the window itself.
 
 On Windows, you can use a taskbar button to display a progress bar.
 
-![Windows Progress Bar][https://cloud.githubusercontent.com/assets/639601/5081682/16691fda-6f0e-11e4-9676-49b6418f1264.png]
+![Windows Progress Bar](../images/windows-progress-bar.png)
 
 On macOS, the progress bar will be displayed as a part of the dock icon.