Added a clarification about a choice not in the choices list causing the field to not validate.
Added a clarification about a choice not in the choices list causing the field to not validate.

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