Document the config options available in config_spec.ini

[rodney757]

It would be nice if we had all of the config options documented in one place.

[Emily O'Leary]

There is a piece of semi-complete documentation in /mediagoblin/mediagoblin/config_spec.ini.

It would just need more comments as to document each option.

[Christopher Allan Webber]

A really simple solution to this: symlink config_spec.ini into the mediagoblin docs' static directoy. Then link to it in the docs somewhere relevant!

[Jorge]

This looks resolved to me.

from docs/source/siteadmin/configuration.rst

There's one more file that you certainly won't change unless you're
making coding contributions to mediagoblin, but which can be useful to
read and reference:

mediagoblin/config_spec.ini
  This file is actually a specification for mediagoblin.ini itself, as
  a config file!  It defines types and defaults.  Sometimes it's a
  good place to look for documentation... or to find that hidden
  option that we didn't tell you about. :)