Symfony 2 form override and path / configuration solving

I'm very new to Symfony 2. I'm trying to add some other custom form fields.

The bundle I'm using has been made this way:

src/TheClient/
`-- Bundle
    |-- MyBundle
    |   |-- Controller
    |   |-- DependencyInjection
    |   |-- Entity
    |   |-- Form
    |   |-- Repository
    |   |-- Resources
    |   `-- Tests
    `-- OtherNotImportantBundle
        |-- Command
        |-- Controller
        |-- DependencyInjection
        |-- Entity
        |-- Resources
        |-- Services
        `-- Tests

I've created the file src/TheClient/Bundle/MyBundle/Resources/views/Form/fields.html.twig where there is some code like this:

{% block form_row %}
    <div class="control-group">
        {{ form_label(form) }}
        {{ form_errors(form) }}
        {{ form_widget(form) }}
    </div>
{% endblock %}

{% block text_widget %}
    <div class="text_widget controls">
        {% set type = type|default('text') %}
        {{ block('form_widget_simple') }}
    </div>
{% endblock %}

To make it short, it overrides the original form ressource to enclose it with div's. Now, what I'm supposed to do is just edit app/config/config.yml and precise the new form fields like this:

# Twig Configuration
twig:
    debug:            %kernel.debug%
    strict_variables: %kernel.debug%
    globals:
      sso_host: %sso_host%
      root_url: %root_url%
    form:
        resources:
            - 'TheClientMyBundle:Form:fields.html.twig'
#            - 'MyBundle:Form:fields.html.twig'

I've tried both solutions and they dont work, I get an error 500. I'm very new to Symfony 2. What are the steps, where should I look, to make it work?

I forgot to precise: I'm trying to follow this tutoriel from the Symfony website itself.

Thank you very much