00-short-intro: Fixed syntax error in "loop"
06-merging-data: ex. code for merging data w/ pandas

Developed some example code showing how to do basic dataframe
merging/joining using pandas; explanatory text to be added later.
06-merging-data: stubbed out explanatory text

Added outline of the text to accompany pandas join/merging code from
previous commit. Definitely not the final product, as it uses jargon and
only briefly explain how various types of joins work (and why we might
want to use them).
Merge pull request #2 from chenghlee/mozsprint-atx

Mozsprint atx