[Components][ClassLoader] documentation for the ClassMapGenerator class

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes (symfony/symfony#2471)
| Applies to    | all
| Fixed tickets | #1134
you need to pass the class map to one of the autoloaders, don't you? Just requiring a file which returns a class map doesn't do anything.