Tour of Jdub

The existing README is great for providing quick examples as briefly as possible, but it can be hard for a newcomer to understand what's going on.

This PR defines a new file with a more detailed explanation of what's going on and how to build your first queries.
"In most cases, you will want your queries to return either a single row or a collection whose items represent each matching row."
 
This is general to the point of meaninglessness. "In most cases, you will want to stand or walk."