First have a look on How to install an Extension to Google wave.
Now
1. Manifest URL is http://haru1ban-wave.googlecode.com/svn/trunk/twitter/manifest.xml
2. Confirm
3. Click Install
4. Install Button will change to uninstall once finished
After install you can add this extension on each new wave
I. Select the right most button (More actions) on the wave
II. Choose My Tweet
5. The extension will display a loading screen
6. Enter your twitter name and number of time lines to display
7. Here is the result
