Add more context and explanation for Lab 2
Add more context and explanation for Lab 2

Added an introduction and explanation of what's
going on in this lab, more information on
databases and SQL (plus obligatory xkcd link).

pdxcat/nixmentors,pdxcat/nixmentors,finchd/nixmentors,blossomica/nixmentors,blossomica/nixmentors,finchd/nixmentors