README

[mallorydxw]

• [ ] Once #6 is merged, it may be useful to explain the new way of doing things as it's different to how it was.
• [ ] I don't understand the difference between app/lib, app/theme, and app/posts. Explain that in the README.
• [ ] Explain what vendor.phar is and how it's generated.
• [ ] Explain where all the "normal" theme stuff is, and why it's not in the root of the theme.
• [ ] Provide a command to use to rename MyTheme to the name of your theme

Use a "I want to do X" style FAQ thingy - that may be easier to write in an understandable manner.