Release documentation

An experiment in documentation.

Adds a documentation directory, /docs/. This is mostly empty for now, since we don't have much documentation. The documentation uses rst <http://docutils.sourceforge.net/rst.html>, the documentation system used by Django, and one of the systems understood and rendered prettily by Github Markup.

This directory has two subdirectories, /docs/dev/ and /docs/admin/. The former is empty for now. The latter is for documentation of the website that we provide to chapter admins with instructions on how to use the website. Much of this information is currently on the LU wiki, but in the future we may choose to migrate it over to version control. Github has a good documentation viewer that is public and requires no login. Maybe in the future we can also build a documentation viewing into all the sites.

The major focus of this pull request is the directory /docs/admin/releases/04. Here lives the static changelog for the release, and can be, if we so choose, distributed to chapters instead of a GDoc / wiki page.