Add img alt texts to wiiu.md

[Kissaki]

Partially resolves/improves #337 - for one page wiiu.md

Changes:

• Add alt text to img links/screenshots for accessibility

• [x] I have read and agreed to the Code of Conduct.

• [x] I have read and complied with the contributing guidelines.

• [x] What I'm implementing was an approved issue.

• [ ] I have tested all of my changes.

[ExperiencersInternational]

Looks good to me apart from a typo of nimble (which isn't actively supported anyways now afaik).

[ashquarky]

Good stuff