README.mkd: Multiple changes to README

* [General Documentation Change] Add section for required third-party software and Python modules.  This is needed if someone wants to set this up in the future on their own, as this isn't detailed in depth and module installation would be a trial-and-error process to get them installed.

* [Critical - Provided Conf Change] Set `check_spam` to 'false' due to observed issues with the Mollom code here, in that the Mollom module no longer has a `MollomAPI` procedure.  Setting (and keeping) `check_spam` as `True` will prevent the application from running, so setting it to `False` by default will allow admins to get the application up and running without a massive amount of errors.

* [Suggested - Provided Conf Change] Set `relay_enabled` to `False` by default in the example config - this is done because it might not be a good idea to turn it on by default until the configuration has been set up and tested.