fix #33: i18next-icu incompatible with react-i18next

[cellog]

I also folded in the fix from #32 to index.d.ts/README.md

Co-Authored-By: Jonas Woerlein 9537926+tngwoerleij@users.noreply.github.com

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

[jamuhl]

was published in i18next-icu@2.0.2

[cellog]

thank you!