Update readme

Author: Greg Bowler

README.md

@@ -1 +1,28 @@
-# Use the Composer CLI in your Github Actions.
+<img src="http://52.48.57.141/php-actions.png" align="right" alt="PHP Actions for Github" />
+
+Use the Composer CLI in your Github Actions.
+==============================================
+
+Composer is a tool for dependency management in PHP. It allows you to declare the libraries your project depends on and it will manage (install/update) them for you.
+
+If you are running tests like [PHPUnit](php-actions-phpunit), [phpspec](php-actions-phpspec) or [Behat](php-actions-behat) in your Github actions, chances are you will need to install your project's dependencies using Composer.
+
+Usage
+-----
+
+Create your Github Workflow configuration in `.github/workflows/ci.yml` or similar.
+
+```yaml
+name: CI
+
+on: [push]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v1
+    - uses: phpactions/composer@master
+    # ... then your own project steps ...
+```