first pass on novice r reference sheet

addresses #663

First pass on the reference sheet.

almost just typed in any function/code I saw

Lots of work to do, but it's a start.
The object is a *data frame*, it has class `"data.frame"`. We should refer to these as *data frames* in normal text. Never concatenate the two words unless with a `.` and then only if we are talling about something pertaining to the *class*.