This patch adds a dummy distributor (and corresponding documentation)
that does the bare minimum to fetch resources from the backend and
distribute them over a Web API.  The dummy distributor has two benefits:

1) It helps newcomers understand the interaction between a distributor
   and the backend.

2) It can serve as a template to speed up the process of implementing a
   new distributor.

This fixes tpo/anti-censorship/rdsys#33.