Use --no-dev when installing

Otherwise the dev requirements *before they are rewritten by the installer* are
used.

Also provides a note detailing how to install the dev requirements after
installation.

README.md

@@ -26,7 +26,7 @@ removed.
 Start your new Expressive project with composer:
 
 ```bash
-$ composer create-project zendframework/zend-expressive-skeleton <project-path>
+$ composer create-project --no-dev zendframework/zend-expressive-skeleton <project-path>
 ```
 
 > ### Release Candidates
@@ -39,9 +39,15 @@ $ composer create-project zendframework/zend-expressive-skeleton <project-path>
 > To install a release candidate, use the following:
 >
 > ```bash
-> $ composer create-project zendframework/zend-expressive-skeleton:^1.0@rc <project-path>
+> $ composer create-project --no-dev "zendframework/zend-expressive-skeleton:^1.0@rc" <project-path>
 > ```
 
+> ### Development requirements
+>
+> If you want Composer to install the development requirements defined by the
+> skeleton — specifically PHPUnit and PHP_CodeSniffer — run a `composer update`
+> after installing the skeleton.
+
 After choosing and installing the packages you want, go to the
 `<project-path>` and start PHP's built-in web server to verify installation: