Added information about supported types to contribution guide.

CONTRIBUTING.md

@@ -6,19 +6,19 @@ If you would like to help, please take a look at the list of
 ## Pull requests
 
 * [Fork and clone](https://help.github.com/articles/fork-a-repo).
-* Run the command `php composer.phar install` to install the dependencies.
-  This will also install the dev dependencies. See [Composer](https://getcomposer.org/doc/03-cli.md#install).
-* Use the command `phpunit` to run the tests. See [PHPUnit](http://phpunit.de).
+* Run the command `php composer.phar install` to install dependencies.
+* Use the command `phpunit` to run the tests.
 * Create a branch, commit, push and send us a
   [pull request](https://help.github.com/articles/using-pull-requests).
 
 To ensure a consistent code base, you should make sure the code follows the
 coding standards [PSR-1](http://www.php-fig.org/psr/psr-1/) and 
 [PSR-2](http://www.php-fig.org/psr/psr-2/).
 
-### Create a new Installer
+## Creating a new Installer
 
-* Create class extends `Composer\Installers\BaseInstaller` with your Installer.
-* Create unit tests as a separate class or as part of a `Composer\Installers\Test\InstallerTest`.
-* Add information about your Installer in `README.md` in section "Current Supported Package Types".
+* Create a class with your Installer that extends `Composer\Installers\BaseInstaller`.
+* Add your Installer to `Composer\Installers\Installer::$supportedTypes`.
+* Create unit tests as a separate class or as part of `Composer\Installers\Test\InstallerTest`.
+* Add information about your Installer to `README.md` in section "Current Supported Package Types".
 * Run the tests.