Clarified steps for new users.

- Expanded the four steps to the discrete steps outlined in the
  document.
- Clarified the steps to use the implied verbs (not "get" but "download
  and install").
- Moved the downloading of the blog skeleton from the "run" section to
  the "download and install" section as it's part of the setup.
- Fixed a couple of spelling mistakes ("let's" is "let us", "lets" is
  "permits")
- Added a space between to the sample twig output to escape the
  variable (and added a note explaining people should take this out).
  Otherwise the variable renders and you get the page title.
- Separated the publish step into two: generate production-ready site;
  and upload to the server.
- Updated the what's next section to point to the documentation, or look
  at examples of what you can build with Sculpin.