Categories Plugin - assign pre-defined categories to annotation and highlight each with different colors. (There is a pull request pending that is not yet fully integrated (waiting for tests)). This does not work with HEAD for now and requires a full check out of the fork (based on a slightly older fork). plugin source code
If you'd like to contribute to the wiki you can do so using the GitHub interface
or a better way is to check out the Wiki and modify it using a text editor.
There's some basic instructions in the Gollum readme.