Add alt text to image

[nielsdB97]

The image showing what technologies i18next will integrate with did not have any descriptive alt text. In order for everyone to be able to learn this information, we should describe what the image contains.

Checklist

• [x] only relevant code is changed (make a diff before you submit the PR)
• [x] run tests npm run test
• [x] tests are included
• [x] documentation is changed or added

[adrai]

great, thx