Fixes#55
The guide is now split into 2 modules:
* `team-info`, which contains our team information
* `contributing`, which contains the actual contributing guide
Each has its own navfile etc. Configs have all been updates so that outwardly, everything looks like it did before (although I did shuffle the table of contents a little bit based on @pboy's suggestions in #55). The default index is now `team-info/index.adoc` (see `antora.yml`); that's the one you'll see when you build the guide - it's the original index.
I also made sure each file has an include for the attributes file and `:experimental:` at the top, and cleaned up the config YMLs a little bit.
Reviewed-on: #63
Reviewed-by: Jan Kuparinen <copperi@noreply.forge.fedoraproject.org>
