Reorganize the README in a webpage export node and the roadmap node.
Reorganize the README in a webpage export node and the roadmap node.

The roadmap only cluttered up the webpage export, so in the future the
README.md used to modify the http://steinarb.github.io/modelstore page
will be exported from one of the README nodes instead of from the entire
README.

steinarb/modelstore,steinarb/modelstore