Documentation wrong about including test-pack and http-client

[RobQuistNL]

The docs here state;

If you don't use the distribution, run composer require --dev symfony/test-pack symfony/http-client to install them.

But this is required even when the project is setup through https://github.com/api-platform/api-platform/generate

[vinceAmstoutz]

@RobQuistNL You're welcome to contribute, check our CONTRIBUTING.md and submit your suggestions. Thanks!