Issue #2168617 by clemens.tolboom: Fix up docs on how to do multisite

core/INSTALL.txt

@@ -328,13 +328,21 @@ MULTISITE CONFIGURATION
 A single Drupal installation can host several Drupal-powered sites, each with
 its own individual configuration.
 
+For this to work you need the file sites/sites.php to exist. Make a copy of
+the example.sites.php file:
+
+  $ cp sites/example.sites.php sites/sites.php
+
 Additional site configurations are created in subdirectories within the 'sites'
 directory. Each subdirectory must have a 'settings.php' file, which specifies
 the configuration settings. The easiest way to create additional sites is to
-copy the 'default' directory and modify the 'settings.php' file as appropriate.
-The new directory name is constructed from the site's URL. The configuration for
-www.example.com could be in 'sites/example.com/settings.php' (note that 'www.'
-should be omitted if users can access your site at http://example.com/).
+copy file 'default.settings.php' from the 'sites/default' directory into the
+new site directory with file name 'settings.php' and modify as appropriate.
+The new directory name is constructed from the site's URL. The configuration
+for www.example.com could be in 'sites/example.com/settings.php' (note that
+'www.' should be omitted if users can access your site at http://example.com/).
+
+  $ cp sites/default/defaults.settings.php sites/example.com/settings.php
 
 Sites do not have to have a different domain. You can also use subdomains and
 subdirectories for Drupal sites. For example, example.com, sub.example.com, and

sites/default/default.settings.php

@@ -10,11 +10,10 @@
  * your modifications. Failure to remove write permissions to this file is a
  * security risk.
  *
- * The configuration file to be loaded is based upon the rules below. However
- * if the multisite aliasing file named sites/sites.php is present, it will be
- * loaded, and the aliases in the array $sites will override the default
- * directory rules below. See sites/example.sites.php for more information about
- * aliases.
+ * In order to use the selection rules below the multisite aliasing file named
+ * sites/sites.php must be present. Its optional settings will be loaded, and
+ * the aliases in the array $sites will override the default directory rules
+ * below. See sites/example.sites.php for more information about aliases.
  *
  * The configuration directory will be discovered by stripping the website's
  * hostname from left to right and pathname from right to left. The first

sites/example.sites.php

@@ -2,22 +2,22 @@
 
 /**
  * @file
- * Configuration file for Drupal's multi-site directory aliasing feature.
+ * Configuration file for multi-site support and directory aliasing feature.
  *
- * This file allows you to define a set of aliases that map hostnames, ports, and
- * pathnames to configuration directories in the sites directory. These aliases
- * are loaded prior to scanning for directories, and they are exempt from the
- * normal discovery rules. See default.settings.php to view how Drupal discovers
- * the configuration directory when no alias is found.
+ * This file is required for multi-site support and also allows you to define a
+ * set of aliases that map hostnames, ports, and pathnames to configuration
+ * directories in the sites directory. These aliases are loaded prior to
+ * scanning for directories, and they are exempt from the normal discovery
+ * rules. See default.settings.php to view how Drupal discovers the
+ * configuration directory when no alias is found.
  *
  * Aliases are useful on development servers, where the domain name may not be
  * the same as the domain of the live server. Since Drupal stores file paths in
  * the database (files, system table, etc.) this will ensure the paths are
  * correct when the site is deployed to a live server.
  *
- * To use this file, copy and rename it such that its path plus filename is
- * 'sites/sites.php'. If you don't need to use multi-site directory aliasing,
- * then you can safely ignore this file, and Drupal will ignore it too.
+ * To activate this feature, copy and rename it such that its path plus
+ * filename is 'sites/sites.php'.
  *
  * Aliases are defined in an associative array named $sites. The array is
  * written in the format: '<port>.<domain>.<path>' => 'directory'. As an