Add missing autoload include for console components page

And better explain where files should be placed in order to be auto-loaded.
@weaverryan let's decide the target audience for the components docs. That always makes a discussion easier than discussing with people all different target audiences in mind.

My target audience for the components docs is 3 people:

* First there are people who are linked to some related usage article (for instance, the Translation usage). These people use the fullstack framework and just want to know usage
* Secondly, the components page attracks people who want to use the component standalone.
* At last, people who want to know more about Symfony internals visit the components articles.

(1) and (3) use the full-stack framework, these autoloading things aren't targeted for one.

Then we are left with (2). I always imagine these people to either already have a project or are at the start of bootstrapping one. They just go to the component docs because they know/found that this component will solve the problem they have.
I think there are almost none users who go the components docs, find a nice component and create a project from it.

The means that these docs are solving the problem of "how to use the component to solve the problem"? That excludes anything related to "how to bootstrap a project?",  "what is the best library structure?" and "how to use Composer?".