doc: update information on how touchscreen users can zoom images

Description

This merge request clarifies to readers that touchscreen users can zoom into images by scrolling and using the control button on their keyboard. By making this change, this demographic would gain a better understanding of how to effectively use this application.

Issue

Closes #312 (closed)

##Note to Reviewers This is my first contribution to this project, so I placed this PR in draft mode for now to get some feedback.