added description to README

Author: co3k

README.rst

@@ -2,6 +2,11 @@
 README
 ======
 
+What is php-dql-tokenizer?
+==========================
+
+This extension is for improving performance of Doctrine_Query_Tokenizer.
+
 INSTALL
 =======
 
@@ -17,6 +22,22 @@ Then add the following to your php.ini::
   [dql_tokenizer]
   extension=dql_tokenizer.so
 
+How To Use
+==========
+
+This extension provides functions that corresponds to the methods of the Doctrine_Query_Tokenizer class.
+
+So you need to define a new tokenizer classes to use this extension.
+
+First, you write the following code in your query class::
+
+  if (function_exists('dql_tokenize_query'))
+  {
+    $this->_tokenizer = new myQueryTokenizer();
+  }
+
+Next, you define a new tokenizer class. You can get the example class file from "example/myQueryTokenizer.class.php".
+
 Credits
 =======