Adds a summary and a link to the wiki for contributors to the front page.
The "what is mediagoblin" section in the about chapter talkd about what
it was, but it was buried--this slightly unburies it.
* create initial bits for plugin writer's guide
* move siteadmin stuff to site administrator's guide
* rework index.rst to support multiple guides
* tweak some text
* move files into subdirectories
I verified that this still works with html and texinfo build targets.
There's still a lot of work to do, but this is a good start.
* Removes a bunch of content that doesn't need to be in the suer manual
anymore.
* Fixes issues so it's more readable in source form.
* Adds help chapter.
* Moves links out of paragraphs to reduce line length.
* Cleans up some language.
* Fixes some links.
- a line in the .gitignore file to ignore the built documentation
tree.
- a complete revision/editorial pass of all non-technical documents
that outline process, project fundamentals, and background. These
edits clarified the text, unified the style, and elaborated on
stubs.
