where you substitute [username] for the actual usename. For example, to subscribe in google reader to Facebook's twitter feed (http://twitter.com/#!/facebook) you click on 'Add a subscription' in reader.google.com and paste in:
There is more documentation on this API at https://dev.twitter.com/docs/api/1/get/statuses/user_timeline. It's listed at the bottom in the 'Extended description' section with the words 'not recommended' :). The 'recommended' API, using URL parameters, doesn't work in google reader. Further note: I initially tried getting RSS feed format to work and didn't have any luck.