Download the zip file (or clone via git) and unzip it.
Double-click the Statamic.tmbundle file or drag it onto the TextMate dock icon.
Enjoy.
Installing On Sublime Text 2
Download the zip file (or clone via git) and unzip it.
Rename Statamic.tmbundle to /Statamic/ (it's just a folder) and drop it in ~/Library/Application Support/Sublime Text 2/Packages/ and drop the Statamic.tmbundle file in it.
Restart Sublime Text 2.
Enjoy.
Note: This is still in development, and has a few kinks to work out. Feel free to fork the repo, tweak it, and make pull requests with your own improvements. The language/highlight syntax isn't super friendly in Sublime yet.