It is possible to directly edit files in a repository stored on GitHub through the web interface. Most of us would never do this but it has its uses.
I think using gist.github.com is the easiest option. Each gist is a Git repository that can be accessed from the web browser or from the shell, there's a comment button, and although gists are usually single files, they can hold multiple files.
The drawbacks to gists are obviously the cryptic URLs and the fact that you have to copy-paste file contents into the browser unless you use a separate tool.