Added README file

README.md

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+# Linku/Feedback
+
+Feedback is an io abstraction that lets you decouple functional code and
+business logic from (CLI) I/O.
+
+## Installation
+
+```
+composer require linku/feedback
+```
+
+## Use
+
+In the class or service you want to decouple, add a `Feedback` attribute
+and make sure it is filled with an instance of `NoFeedback` by default.
+
+In order to allow the code calling this service to override the default
+feedback, add a `setFeedback` method.
+
+In the logic of your service, you can now call the feedback methods.
+
+```php
+<?php
+
+use Linku\Feedback\Feedback;
+use Linku\Feedback\NoFeedback;
+
+class MyService
+{
+    /**
+     * @var Feedback
+     */
+    private $feedback;
+
+    public function __construct()
+    {
+        $this->feedback = new NoFeedback();
+    }
+
+    public function setFeedback(Feedback $feedback): void
+    {
+        $this->feedback = $feedback;    
+    }
+
+    public function run(): void
+    {
+        $this->feedback->info('Starting my service run');
+
+        $this->feedback->startProcess();
+
+        for ($i = 0; $i < 100; $i++) {
+            try {
+                // Do something in a loop here
+            } catch (\Throwable $exception) {
+                $this->feedback->exception($exception);
+            }
+
+            $this->feedback->advanceProcess();
+        }
+
+        $this->feedback->finishProcess();
+
+        $this->feedback->success('Completed my service run');
+    }
+}
+```
+
+In the script or CLI command that uses your service, set the apropriate
+feedback.
+
+```php
+<?php
+
+$service = new MyService();
+
+$service->setFeedback(new LoggerFeedback(new Logger()));
+
+$service->run();
+```
+
+## Available feedback
+### NoFeedback
+A safe fallback that doesn't output anything.
+
+### ClosureFeedback
+A feedback you can fill with your own anonymous functions.
+
+### LoggerFeedback
+A feedback that will write to any PSR-3 Logger.
+
+### ChainedFeedback
+A feedback that lets you use multiple feedbacks at the same time.
+```php
+<?php
+
+$myService->setFeedback(new ChainedFeedback(
+    new LoggerFeedback(new Logger()),
+    new ClosureFeedback(/* ... */)
+));
+```
+
+## Other feedback packages
+### SymfonyStyleFeedback
+If you use Symfony CLI, check out [LinkuNijmegen/SymfonyStyleFeedback](https://github.com/linkunijmegen/SymfonyStyleFeedback)
+for integration with the Symfony Style component.