Update the slim4 example please.

[Danack]

Currently the example in the Slim4 branch doesn't work due to

$app = new Slim\App();

requires changing to something like:

$psrFactory = new Psr17Factory();
$app = new Slim\App(
    $psrFactory
);

The run line also needs changing, as:

$app->run();

requires a request to be passed in. However I can't seem to see an obviously correct way of doing that. Any suggestion please.

[akrabat]

#2529 currently has the best explanations of how to run the Slim 4.x branch.

[akrabat]

@Danack Example now works. Note that you don't have to use that PSR-7 implementation though.