Hi khaled,
I don't think there is a document for that yet, but installing the plugin is not that difficult. You can find instructions here:
Those instructions are:
- Intallation
The plugin is hosted on the IntelliJ IDEA Plugin Repository. To download and install the plugin, follow these steps:
1. Install IntelliJ IDEA 11 (either the Ultimate or Community editions) to your machine
2. With IntelliJ running, open the Settings menu and select Plugins
3. Click the Browse Repositories... button, and search for gosu
4. Right click on the Gosu plugin and select Download and Install
5. After the plugin has been installed, restart IntelliJ
Concerning your problem, to make it run, it is probably solved by 1 (or both) answers here below that you can find on the same page mentioned above:
FAQ
Q: I created a new project but can't find the action to create new Gosu files, where are they?
A: Make sure you created a package first, then right-click on it and and select New/Gosu Class
Q: Gosu does not seem to work properly in my project, but I cannot see why.
A: Make sure you have the Default Gosu SDK set on your project (File/Project Structure/Project)."
Hope that helps
Best regards
Carlos