Merge pull request #12 from jawira/update_getting_started

fix: Update "Getting Started" commands

Author: skoro

README.md

@@ -25,6 +25,7 @@ Clone this repository and try out the demos:
 ```sh
 git clone https://github.com/skoro/php-tkui.git php-tkui
 cd php-tkui
+composer install
 php demos/buttons.php
 ```