Add examples to README

Could you add examples to README?

## My idea
### Input
`mocha.opts`:

```
--require ts-node/register
--reporter spec
--recursive
```

### Output
`.mocharc.json`:

```json
{
"require": [
"ts-node/register"
],
"reporter": "spec",
"recursive": true
}
```

`.mocharc.js`:

```js
(module.exports = {
"require": ["ts-node/register"],
"reporter": "spec",
"recursive": true
})
```

`.mocharc.yml` or `.mocharc.yaml`:

```yaml
---
require:
- "ts-node/register"
reporter: "spec"
recursive: true
```

For showing examples of several types, it's using...

- `require` (for array)
- `reporter` (for string)
- `recursive` (for boolean)

But there may be other better examples.

Start by reading the README and locate the section describing mocha.opts migration. Add the supplied configuration examples, or refine them to cover array, string, and boolean values, then consider the work done when the README clearly shows the corresponding .mocharc.json, .mocharc.js, and .mocharc.yml or .mocharc.yaml formats.

Written by the indexing model from the issue text.