minor #17997 Updated all the README files (javiereguiluz)

This PR was squashed before being merged into the 2.3 branch (closes #17997).

Discussion
----------

Updated all the README files

| Q             | A
| ------------- | ---
| Branch        | 2.3
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Related to #17995.

Commits
-------

2e81248 Updated all the README files

Author: fabpot

README.md

@@ -1,99 +1,16 @@
 HttpKernel Component
 ====================
 
-HttpKernel provides the building blocks to create flexible and fast HTTP-based
-frameworks.
-
-``HttpKernelInterface`` is the core interface of the Symfony full-stack
-framework:
-
-```php
-interface HttpKernelInterface
-{
-    /**
-     * Handles a Request to convert it to a Response.
-     *
-     * @param Request $request A Request instance
-     *
-     * @return Response A Response instance
-     */
-    function handle(Request $request, $type = self::MASTER_REQUEST, $catch = true);
-}
-```
-
-It takes a ``Request`` as an input and should return a ``Response`` as an
-output. Using this interface makes your code compatible with all frameworks
-using the Symfony components. And this will give you many cool features for
-free.
-
-Creating a framework based on the Symfony components is really easy. Here is
-a very simple, but fully-featured framework based on the Symfony components:
-
-```php
-$routes = new RouteCollection();
-$routes->add('hello', new Route('/hello', array('_controller' =>
-    function (Request $request) {
-        return new Response(sprintf("Hello %s", $request->get('name')));
-    }
-)));
-
-$request = Request::createFromGlobals();
-
-$context = new RequestContext();
-$context->fromRequest($request);
-
-$matcher = new UrlMatcher($routes, $context);
-
-$dispatcher = new EventDispatcher();
-$dispatcher->addSubscriber(new RouterListener($matcher));
-
-$resolver = new ControllerResolver();
-
-$kernel = new HttpKernel($dispatcher, $resolver);
-
-$kernel->handle($request)->send();
-```
-
-This is all you need to create a flexible framework with the Symfony
-components.
-
-Want to add an HTTP reverse proxy and benefit from HTTP caching and Edge Side
-Includes?
-
-```php
-$kernel = new HttpKernel($dispatcher, $resolver);
-
-$kernel = new HttpCache($kernel, new Store(__DIR__.'/cache'));
-```
-
-Want to functional test this small framework?
-
-```php
-$client = new Client($kernel);
-$crawler = $client->request('GET', '/hello/Fabien');
-
-$this->assertEquals('Fabien', $crawler->filter('p > span')->text());
-```
-
-Want nice error pages instead of ugly PHP exceptions?
-
-```php
-$dispatcher->addSubscriber(new ExceptionListener(function (Request $request) {
-    $msg = 'Something went wrong! ('.$request->get('exception')->getMessage().')';
-
-    return new Response($msg, 500);
-}));
-```
-
-And that's why the simple looking ``HttpKernelInterface`` is so powerful. It
-gives you access to a lot of cool features, ready to be used out of the box,
-with no efforts.
+The HttpKernel component provides a structured process for converting a Request
+into a Response by making use of the EventDispatcher component. It's flexible
+enough to create a full-stack framework (Symfony), a micro-framework (Silex) or
+an advanced CMS system (Drupal).
 
 Resources
 ---------
 
-You can run the unit tests with the following command:
-
-    $ cd path/to/Symfony/Component/HttpKernel/
-    $ composer install
-    $ phpunit
+  * [Documentation](https://symfony.com/doc/current/components/http_kernel/index.html)
+  * [Contributing](https://symfony.com/doc/current/contributing/index.html)
+  * [Report issues](https://github.com/symfony/symfony/issues) and
+    [send Pull Requests](https://github.com/symfony/symfony/pulls)
+    in the [main Symfony repository](https://github.com/symfony/symfony)