Why would I attach things to a wiki?
The most common example of when you would attach something to a wiki would be when you need an image in the wiki page and you're concerned that if the image is hosted remotely (a corporate web server, for exampe), it might be moved or removed. Additionally, you might wish to attach a file to a wiki page if the attachment is only truly important in the context of the wiki page and therefore isn't important enough to be uploaded to the Document Manager of SourceForge.
How do I edit the wiki home page?
Once you've enabled the wiki as the project home page option in Project Admin, you must return to the project home page by clicking the Project Home button. There will be an Edit button on the bottom right of the page under the graphs. You may need to scroll your browser window to the right to see this button.
I set my project to "use wiki homepage" so why isn't my wiki showing up?
SourceForge currently uses two distinctly different wikis. There is the wiki you've already edited, which is available by clicking on the Wiki button at the top of any project page, and there is the "project home" wiki, which is what you enabled in the Project Admin screen. If you visit the project home page after setting this option, and you have the proper RBAC permissions, there should be an Edit button in the bottom-right corner of the home page under the graphs. Use this button to edit the project home page wiki.