Add details on how to contribute to the README.md

This closes https://trac.torproject.org/projects/tor/ticket/11980
Add a tool for generating ooniprobe decks.

* Also adds tool for downloading ooniprobe resources.
Add oonideckgen and ooniresources to setup.py
Make the update-inputs command an option
Read the config file before running cli.
Add support for downloading GeoIP files via the ooniresource tool.

* Add better exception handling to ooniresource.
* Add gunzip to utils.
Add notice about using ooniresources to download geoip files.
Improvements to the installation and usage guide

* Add section describing how to generate decks
* Add usage information for ooniresources
* Add a guide on getting up and running with ooniprobe in 5 minutes
* Move the development environment setup guide down