Based off of https://github.com/mattt/Xcode-Snippets
In Xcode 4, open a workspace and toggle the right sidebar to be visible. On the bottom, there is a panel with four icons in the header. Click on the { } icon to open the Code Snippets Library.
Now copy-paste the code from one of these snippets, highlight the code block you just pasted and drag it to the Code Snippet panel. Make sure to match the suggested platform, language, and completion scope. The completion shortcut corresponds to the filename of the code snippet.