add docs on how to nest properly
add docs on how to nest properly

closes #126

lok0613/jquery-sortable,farindra/jquery-sortable,leafiy/jquery-sortable,leafiy/jquery-sortable,Youraiseme/jquery-sortable,migueldanto/jquery-sortable,lok0613/jquery-sortable,Youraiseme/jquery-sortable,leafiy/jquery-sortable,Youraiseme/jquery-sortable,lok0613/jquery-sortable,leafiy/jquery-sortable,migueldanto/jquery-sortable,farindra/jquery-sortable,farindra/jquery-sortable,farindra/jquery-sortable,lok0613/jquery-sortable,migueldanto/jquery-sortable,migueldanto/jquery-sortable,Youraiseme/jquery-sortable