Fix link to todo.txt format

[donovanglover]

I knew I missed something. Changed the todo.txt format link so it links directly now.

Some other things I noticed (I'm tagging this with #1, but ideally there should be a list of all the things we want to do and a milestone for it):

• The website often changes between todo.txt and Todo.txt. Which one do we want to use?
• Instead of linking to a todo.txt file, it would be much better IMO if we included an example on the homepage itself (with syntax highlighting!) Why?
  • At the end of the day, it's still a plain text file. You can do whatever you want with it, colors included.
  • Most tools use color coding anyway, so it's a more accurate representation of how you'll actually use your todo.txt file.

[karbassi]

Great idea @GloverDonovan. Here it is: https://github.com/todotxt/todotxt.github.io/milestone/1