README: nginx: Added description for subrole default_server

README.md

@@ -38,6 +38,7 @@ Following roles have been defined for making a server configuration easy:
   - **database** configures a database for an external application with its own user (uses **mysql/backup_database**)
 - **nginx** defines roles to set up virtual servers, certificates will be requested by default
   - **application** installs and configures the main requirements
+  - **default_server** configures default server for hostname fqdn with status info (only accessable from localhost)
   - **forward** sets up a forwarding from one domain to another
   - **php** sets up a PHP webpage with files at the given directory
   - **php-fpm** installs php-fpm and requirements