README references non-existent 'test:run' script

## Description

The README references `yarn test:run` but this script doesn't exist in `package.json`. The correct command is `yarn test`.

## Steps to reproduce

```bash
yarn test:run
```

Results in:
```
Usage Error: Couldn't find a script named "test:run".
```

## Suggested fix

Update the README to use `yarn test` instead of `yarn test:run`.