modify INSTALL to provide more configuration info

Suggest updating the "Drupal Administration" section of INSTALL to provide some additional information on configuring a Drupal site.

Suggested revision follows:

DRUPAL ADMINISTRATION
---------------------

Upon a new installation, your Drupal website defaults to a very basic configuration with only a few active modules, one theme, and no user access rights.

Use your administration panel to enable and configure services. For example, set some general settings for your site with Administration » site configuration. Enable modules via Administration » site configuration » modules. User permissions can be set with Administration » user management » user permissions.

For more information on configuration options, read through the instructions which accompany the different configuration settings and consult the various help pages available in the administration panel.

Note that additional community-contributed modules and themes are available at drupal.org.