Cleaner install instruction without curl

doc/00-intro.md

@@ -119,7 +119,7 @@ Change to a directory on your `PATH` and run the install snippet to download
 composer.phar:
 
     C:\Users\username>cd C:\bin
-    C:\bin>php -r "eval('?>'.file_get_contents('https://getcomposer.org/installer'));"
+    C:\bin>php -r "readfile('https://getcomposer.org/installer');" | php
 
 > **Note:** If the above fails due to file_get_contents, use the `http` url or enable php_openssl.dll in php.ini