updated intro and basic-usage to reflect new --install-dir option

doc/00-intro.md

@@ -45,6 +45,11 @@ composer:
 This will just check a few PHP settings and then download `composer.phar` to
 your working directory. This file is the composer binary.
 
+You can install composer to a specific directory by using the `--install-dir`
+option and providing a target directory (it can be an absolute or relative path):
+
+    $ curl -s http://getcomposer.org/installer | php -- --install-dir=bin
+
 After that we run the command for installing all dependencies:
 
     $ php composer.phar install

doc/01-basic-usage.md

@@ -18,6 +18,11 @@ You can place this file anywhere you wish. If you put it in your `PATH`,
 you can access it globally. On unixy systems you can even make it
 executable and invoke it without `php`.
 
+You can install composer to a specific directory by using the `--install-dir`
+option and providing a target directory (it can be an absolute or relative path):
+
+    $ curl -s http://getcomposer.org/installer | php -- --install-dir=bin
+
 To check if composer is working, just run the PHAR through `php`:
 
     $ php composer.phar