Added installation instructions for #19 (#20)

* Added installation instructions

* Added docker as recommended installation method

Author: Drachenkaetzchen

README.md

@@ -3,3 +3,28 @@ API Platform Demo
 
 This a demonstration application for the [API Platform Framework](https://api-platform.com).
 Try it online at <https://demo.api-platform.com>.
+
+Installation (recommended)
+==========================
+
+```shell
+
+$ git clone https://github.com/api-platform/demo.git
+
+
+$ docker-compose up
+```
+
+Installation (manual)
+=====================
+
+```shell
+
+$ git clone https://github.com/api-platform/demo.git
+
+$ composer install
+
+# Create a user and a database in MySQL and enter the credentials during composer install
+
+$ php bin/console doctrine:schema:update --force
+```