Add key and cert and hostname params to example config in README.md

[aacic]

As explained here:

https://github.com/cameronhunter/local-ssl-proxy/issues/113

Using a config.json per the instructions fails:

{
  "My proxy": {
    "source": 3001,
    "target": 3000
  },
  "Another proxy": {
    "source": 9999,
    "target": 9000
  }
}

I've updated the config in README.MD to:

{
  "My proxy": {
    "source": 3001,
    "target": 3000,
    "key": "localhost-key.pem",
    "cert": "localhost.pem",
    "hostname": "localhost"
  },
  "Another proxy": {
    "source": 9999,
    "target": 9000,
    "key": "localhost-key.pem",
    "cert": "localhost.pem",
    "hostname": "localhost"
  }
}

[cameronhunter]

Thanks for the contribution!