Embrace a single file, readme.md, to avoid ambiguity

Instead of suggesting a file, then `readme.md`, and then "your .txt file", this just proposes a single file—the readme. What's cool about this is that we can subtly show them more benefits of GitHub—Markdown, a cool project info dealie (the rendered readme itself), and it's more 1337 hackerish.

We could also do `.txt` though if it's a tad too much this early in the game. Your call completely—just felt like this simplified a few things.