Parsons to teach indentation

[reingart]

Chapter about indentation has no interactive activity:

https://pyar.github.io/PyZombis/main/lectures/TWP30/TWP30_2.html

Add a Pearson exercise to illustrate concepts and self-assessment:
https://runestone.academy/ns/books/published/authorguide/directives/parsons.html

Sample (please modify with the examples in the chapter):

.. parsonsprob:: par_ex_group1

   Construct a function that returns the max value from a list.
   -----
   def findmax(alist):
       if len(alist) == 0:
           return None
       curmax = alist[0]
       for item in alist:
           if item > curmax:
               curmax = item
       return curmax