Use best practice for adding this library as a dependency using Composer

Author: sebastianbergmann

README.md

@@ -6,10 +6,11 @@ Snapshotting of global state, factored out of PHPUnit into a stand-alone compone
 
 ## Installation
 
-To add this package as a local, per-project dependency to your project, simply add a dependency on `sebastian/global-state` to your project's `composer.json` file. Here is a minimal example of a `composer.json` file that just defines a dependency on GlobalState:
+You can add this library as a local, per-project dependency to your project using [Composer](https://getcomposer.org/):
+
+    composer require sebastian/global-state
+
+If you only need this library during development, for instance to run your project's test suite, then you should add it as a development-time dependency:
+
+    composer require --dev sebastian/global-state
 
-    {
-        "require": {
-            "sebastian/global-state": "1.0.*"
-        }
-    }