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

[nestordedios]

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