Added instructions to README for installing with composer.

Author: joachim-n

README.md

@@ -3,13 +3,23 @@ Drupal Code Builder library.
 
 ## Installation
 
-1. Place this folder somewhere where Drush will locate it as a command. (See
-  http://docs.drush.org/en/8.x/commands/#create-commandfiledrushinc for
-  possible locations.)
-2. Do `composer require drupal-code-builder/drupal-code-builder` in the Drush
-  installation folder.
-3. Do `drush cc drush` to rebuild Drush's cache of commands.
-4. Do `drush mb-download` in your Drupal site. This detects hooks, services, and
+There are two ways to install this command:
+
+- Composer installation as a Drush extension
+  1. Do `composer require drupal-code-builder/drupal-code-builder-drush:^8.0.0`
+    to install this package and its dependencies. You will need your project to
+    use drupal-composer/drupal-project, or have your composer.josn configured
+    to place Drush extensions into drush/contrib.
+- Manual installation as Drush extension
+  1. Place this somewhere Drush will locate it as a command, such as
+    drush/contrib.
+  2. Do `composer require drupal-code-builder/drupal-code-builder` to install
+    the Drupal Coder Builder library.
+
+Once this is installed:
+
+1. Do `drush cc drush` to rebuild Drush's cache of commands.
+2. Do `drush mb-download` in your Drupal site. This detects hooks, services, and
   plugin types in your Drupal site's codebase and analyses them for use with
   Drupal Code Builder.