Add how to use tab.

[svalqui]

Address Issue #93
@benflips does this resembles what you were thinking about? I can add pictures to each section.

[benflips]

Thanks @svalqui . That's a good start. I also want to add some thoughts about how to interpret things. I can do that later.

Note, @melissamakin123 just made some nice changes to the tab structure (it doesn't exist anymore). So integration of the .Rmd will be different. Let's make "How to" the last section (after About). If you can make that adjustment, I'll turn it into a branch and make additions to the .Rmd.