Add README to text recognition module

## Description
We're missing a `README.md` inside of `modules/react-native-mlkit-text-recognition`, which will show up on npm's listing

## Visuals

<img width="805" height="574" alt="Image" src="https://github.com/user-attachments/assets/43195dc6-bfc2-4ad4-8aac-452f0ea156ba" />