add perfomance chapters

implementation/18-caching/data/pages/02-composer.md

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+[<< previous](01-front-controller.md) | [next >>](03-error-handler.md)
+
+### Composer
+
+[Composer](https://getcomposer.org/) is a dependency manager for PHP.
+
+Just because you are not using a framework does not mean you will have to reinvent the wheel every time you want to do
+something. With Composer, you can install third-party libraries for your application.
+
+If you don't have Composer installed already, head over to the website and install it. You can find Composer packages
+for your project on [Packagist](https://packagist.org/).
+
+Create a new file in your project root folder called `composer.json`. This is the Composer configuration file that will
+be used to configure your project and its dependencies. It must be valid JSON or Composer will fail.
+
+Add the following content to the file:
+
+```json
+{
+  "name": "lubian/no-framework",
+  "require": {
+    "php": "^8.1"
+  },
+  "autoload": {
+    "psr-4": {
+      "Lubian\\NoFramework\\": "src/"
+    }
+  },
+  "authors": [
+    {
+      "name": "lubiana",
+      "email": "lubiana@hannover.ccc.de"
+    }
+  ]
+}
+```
+
+In the autoload part you can see that I am using the `Lubian\NoFramework` namespace for the project. You can use
+whatever fits your project there, but from now on I will always use the `Lubian\NoFramework` namespace in my examples.
+Just replace it with your namespace in your own code.
+
+I have also defined, that all my code and classes in the 'Lubian\NoFramework' namespace lives under the './src' folder.
+
+As the Bootstrap.php file is placed in that directory we should
+add the namespace to the File as well. Here is my current Bootstrap.php
+as a reference:
+
+```php
+<?php declare(strict_types=1);
+
+namespace Lubian\NoFramework;
+
+echo 'Hello World!';
+```
+
+
+Open a new console window and navigate into your project root folder. There run `composer update`.
+
+Composer creates a `composer.lock` file that locks in your dependencies and a vendor directory. 
+
+Committing the `composer.lock` file into version control is generally good practice for projects. It allows
+continuation testing tools (such as [Travis CI](https://travis-ci.org/)) to run the tests against the exact same
+versions of libraries that you're developing against. It also allows all people who are working on the project to use
+the exact same version of libraries i.e. it eliminates a source of "works on my machine" problems.
+
+
+That being said, [you don't want to put the actual source code of your dependencies in your git repository](https://getcomposer.org/doc/faqs/should-i-commit-the-dependencies-in-my-vendor-directory.md). So let's add a rule to our `.gitignore` file:
+
+```
+vendor/
+```
+
+Now you have successfully created an empty playground which you can use to set up your project.
+
+[<< previous](01-front-controller.md) | [next >>](03-error-handler.md)