Update README.

Author: jhedstrom

README.md

@@ -1,3 +1,9 @@
 [![Build Status](https://travis-ci.org/drupal-composer/info-rewrite.svg?branch=master)](https://travis-ci.org/drupal-composer/info-rewrite)
 
 A composer plugin for rewriting Drupal `.info`/`.info.yml` files to include version information that Drupal requires.
+
+This is only required when downloading projects that aren't full releases (for instance, dev versions).
+
+## Installation
+
+`composer require drupal-composer/info-rewrite:~1.0`