Reorganize the documentation

Will close issue #257 and #273 
Right above this line (not changed in this PR), we have:

```bash
$ php composer.phar require vich/uploader-bundle 'dev-master'
```

I think we should remove the `$` (I see people copy it at times) and give them a better version:

```bash
php composer.phar require vich/uploader-bundle ~0.9.0
```

Eventually, (see composer/composer#3096), we can even leave off the version number.