Homepage: point SocketStream link to GitHub's readme.

The current SocketStream example is pointing to a plain text representation of the markdown at [todomvc.com/labs/architecture-examples/socketstream/README.md](http://todomvc.com/labs/architecture-examples/socketstream/README.md)

I switched the link to point to [github.com/addyosmani/todomvc/blob/gh-pages/labs/architecture-examples/socketstream/README.md](https://github.com/addyosmani/todomvc/blob/gh-pages/labs/architecture-examples/socketstream/README.md), so the user is in the right spot to see the code being discussed.