Add alt texts properly in the style guide

[malvikasharan]

Summary

Updating the style guide for images

List of changes proposed in this PR (pull-request)

• Corrects some errors in the style guide for images
• Adds a paragraph additionally on Alt text
• Improves alt text examples

What should a reviewer concentrate their feedback on?

• Everything looks ok?

Acknowledging contributors

• All contributors to this pull request are already named in the table of contributors in the README file.
• The following people should be added to the table of contributors in the README file:

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[BeastyBlacksmith]

Well done!

[malvikasharan]

Thank you @BeastyBlacksmith 🎉