Add documentation for country "point of view" work

[stepps00]

Through whosonfirst-data/whosonfirst-data#1930, Who's On First will gain new records, properties, and geometries at the country and disputed placetypes. Let's add documention about:

• New properties being added to these records (with links to new whosonfirst-properties json files)
• How the Makefile works to create default and alt geoms
• A general description of what work was done, so the work can be repeated in the future

The Makefile should also be added to this repo.

[thisisaaronland]

Also, blog post!