[Bolt 4] Document bin/console bolt:setup with --no-fixtures and --fixtures options

In the current Docs you can setup a project running:

```
# In one go
bin/console bolt:setup

# As separate steps
bin/console doctrine:database:create
bin/console doctrine:schema:create
bin/console bolt:add-user --admin
bin/console doctrine:fixtures:load
```

We could also mention that the options `--no-fixtures` and `--fixtures` exist to add or not dummy content.

`bin/console bolt:setup --no-fixtures`
`bin/console bolt:setup --fixtures`