move documentation markdown to system directory.

laravel/documentation/config.md

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+# Runtime Configuration
+
+## Contents
+
+- [The Basics](#the-basics)
+- [Retrieving Options](#retrieving-options)
+- [Setting Options](#setting-options)
+
+<a name="the-basics"></a>
+## The Basics
+
+Sometimes you may need to get and set configuration options at runtime. For this you'll use the **Config** class, which utilizes Laravel's "dot" syntax for accessing configuration files and items.
+
+<a name="retrieving-options"></a>
+##  Retrieving Options
+
+#### Retrieve a configuration option:
+
+	$value = Config::get('application.url');
+
+#### Return a default value if the option doesn't exist:
+
+	$value = Config::get('application.timezone', 'UTC');
+
+#### Retrieve an entire configuration array:
+
+	$options = Config::get('database');
+
+<a name="setting-options"></a>
+## Setting Options
+
+#### Set a configuration option:
+
+	Config::set('cache.driver', 'apc');