docs(02-faq.md): fakeLoader usage

[rbalet]

Tested it locally, () => new FakeLoader() is incorrect.

Note: a global fakeLoader need to be created in the project himself

const translations: TranslationObject = { TEST: 'This is a test' }
const fakeTranslation: TranslationObject = { NOT_USED: 'not used' }

@Injectable()
export class FakeLoader implements TranslateLoader {
  getTranslation(lang: string): Observable<TranslationObject> {
    if (lang === 'fake') {
      return of(fakeTranslation)
    }

    return of(translations)
  }
}