Updated cakephp overview + added notes on every non-translated page (spanish translations)

I've [asked lorenzo](https://github.com/elboletaire/docs/commit/8ac89cf8e974da4962267a673834e5fe7919bbdf#commitcomment-7502823) if it would be a good idea to add every non-translated english page into the spanish documentations with the same notes I've added for non-updated files.

The note is as follows:

```
.. note::
    Esta página todavía no ha sido traducida y pertenece a la documentación de
    CakePHP 2.X. Si te animas puedes ayudarnos `traduciendo la documentación
    desde Github <https://github.com/cakephp/docs>`_.
```

And says something like:


```
.. note::
    This page hasn't been translated yet; it belongs to CakePHP 2.X docs. If you
    dare, you can help us 
    `translating the docs from Github <https://github.com/cakephp/docs>`_.
```

What do you think? May I copy non-existent files to the spanish docs adding that note? I think it would be a good Idea to have both documentations as close as possible. They would offer the same in every language, maiking it more more easily to maintain and I also think that more people could be engaged for translating docs if they see the documentation mid-translated.