updated readme.

readme.md

-Yii 2 Web Programming Framework
-===============================
+Yii PHP Framework Version 2
+===========================
 
-Thank you for choosing Yii 2 — a high-performance component-based PHP framework.
+Thank you for choosing Yii - a high-performance component-based PHP framework.
 
+If you are looking for a production-ready PHP framework, please use
+[Yii v1.1](https://github.com/yiisoft/yii).
+
+Yii 2 is still under heavy development. We may make significant changes
+without prior notices. **Yii 2 is not ready for production yet.**
 
-INSTALLATION
-------------
 
-Please make sure the release file is unpacked under a Web-accessible
-directory. You shall see the following files and directories:
+DIRECTORY STRUCTURE
+-------------------
 
-      demos/               demos
+      app/                 a ready-to-use application built on Yii 2
+      build/               internally used build tools
+      docs/                documentation
       framework/           framework source files
-      requirements/        requirement checker
-      changelog.md         describing changes in every Yii release
-      license.md           license of Yii
-      readme.md            this file
-      upgrade.md           upgrading instructions
+      tests/               tests of the core framework code
 
 
 REQUIREMENTS
 ------------
 
-The minimum requirement by Yii is that your Web server supports
-PHP 5.3.8 or above. Yii has been tested with Apache HTTP server
-on Windows and Linux operating systems.
-
-Please access the following URL to check if your Web server reaches
-the requirements by Yii, assuming "YiiPath" is where Yii is installed:
-
-      http://hostname/YiiPath/requirements/index.php
-
-
-QUICK START
------------
-
-Yii comes with a command line tool called "yiic" that can create
-a skeleton Yii application for you to start with.
-
-On a command line, type in the following commands:
-
-   for Linux
-        $ cd YiiPath/framework
-        $ ./yiic webapp ../testdrive
-
-   for Windows
-        cd YiiPath\framework
-        yiic webapp ..\testdrive
-
-The new Yii application will be created at "YiiPath/testdrive".
-You can access it with the following URL:
+The minimum requirement by Yii is that your Web server supports PHP 5.3.?.
 
-        http://hostname/YiiPath/testdrive/index.php
 
+HOW TO PARTICIPATE
+------------------
 
-WHAT's NEXT
------------
+You are welcome to participate in Yii 2 development in the following ways:
 
-Please visit the project website for tutorials, class reference
-and join discussions with other Yii users.
+* [Report issues](https://github.com/yiisoft/yii2/issues)
+* [Give us feedback or start a design discussion](http://www.yiiframework.com/forum/index.php/forum/42-design-discussions-for-yii-20/)
+* Fix issues, develop features, write/polish documentation
+    - Before you start, please adopt an existing issue or start a new one to avoid duplicated efforts.
+    - Please submit a merge request after you finish development.