Updates and fixes the "Loading Content From A File" lesson in "Getting Started" tutorial
This MR updates code templates, indents code according to these templates, fixes critical C error, updates the accompanying text, and includes updated images in both light and dark variants.
This is cherry-picked form !135 (closed) and updated, and can be merged right away. As with every one of these MRs, I've tested each step in the tutorial in each language — it works (now).