Tutorial: add an auto_populate example.
Tutorial: add an auto_populate example.

hsum/wtforms,crast/wtforms,jmagnusson/wtforms,Aaron1992/wtforms,skytreader/wtforms,Aaron1992/wtforms,subyraman/wtforms,Xender/wtforms,pawl/wtforms,cklein/wtforms,pawl/wtforms,wtforms/wtforms