Put note in documentation about app key.

installation.md

@@ -49,7 +49,9 @@ As of PHP 5.5, some OS distributions may require you to manually install the PHP
 <a name="configuration"></a>
 ## Configuration
 
-Laravel needs almost no configuration out of the box. You are free to get started developing! However, you may wish to review the `app/config/app.php` file and its documentation. It contains several options such as `timezone` and `locale` that you may wish to change according to your application.
+**The first thing you should do after installing Laravel is set your application key to a random string. Typically, this string should be 32 characters long. The key can be set in the `app.php` configuration file.**
+
+Laravel needs almost no other configuration out of the box. You are free to get started developing! However, you may wish to review the `app/config/app.php` file and its documentation. It contains several options such as `timezone` and `locale` that you may wish to change according to your application.
 
 Once Laravel is installed, you should also [configure your local environment](/docs/configuration#environment-configuration). This will allow you to receive detailed error messages when developing on your local machine. By default, detailed error reporting is disabled in your production configuration file.