Update ConfigurationFile.md (#3320)
Update ConfigurationFile.md (#3320)

## Proposed changes

We only have only one option
```
? Where should your tests be launched
>  local - https://www.npmjs.com/package/@wdio/local-runner

```
And without ```runner: 'local'``` in the configuration file caused the test failure (sync mode )
So I think we better add the into the sample configuration

## Types of changes

- [ ] Bugfix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
- [x] Documentation update

## Checklist

- [x] I have read the [CONTRIBUTING](https://github.com/webdriverio/webdriverio/blob/master/CONTRIBUTING.md) doc
- [ ] I have added tests that prove my fix is effective or that my feature works
- [ ] I have added necessary documentation (if appropriate)

### Reviewers: @webdriverio/technical-committee

klamping/webdriverio,webdriverio/webdriverio,klamping/webdriverio,klamping/webdriverio,webdriverio/webdriverio,webdriverio/webdriverio