completed documentation

README.md

 ## Description
 
-This role installs, enables and configures the PHP module `<module>`.
+This role installs, enables and configures the PHP PDO module for `mysql`.
 
 ## Requirements
 
 ### Variables
 
+* php_mod_pdo_mysql_default_socket
+  * description:
+    * This option specifies the Unix domain socket. 
+  * default: "/tmp/mysql.sock"
+
+* php_mod_pdo_mysql_debug
+  * description:
+    * This option enables debugging for PDO_MYSQL.
+    * It is available when PDO_MYSQL is compiled against mysqlnd and in PDO debug mode.
+  * default:
+
 ## Processes
 
 None