Document the public bindings provided by modules

To document a Ray.Di module, a good strategy is to describe the public bindings that that module installs, for example:

/**
 * Provides FooServiceClient and derived bindings
 *
 * [...]
 *
 * The following bindings are provided:
 *
 *  FooServiceClient
 *  FooServiceClientAuthenticator
 */
final class FooServiceClientModule extends AbstractModule
{
  // ...
}