Update README with the install recommendations of hubot

Like mention when using the previous commands
```bash
$ hubot --create .
'hubot --create' is depreated. Use the yeoman generator instead:
    npm install -g yo generator-hubot
    mkdir -p .
    yo hubot
   See https://github.com/github/hubot/blob/master/docs/README.md for more details on getting started.
```

Maybe it's a good idea to change the README ?

Tell me