add questions and answers for each unit

[satra]

we could take a look at: https://classroom.github.com/

[djarecka]

@satra : have you started using it? do you have any examples?

[satra]

i was planning on using this type of thing:

http://swcarpentry.github.io/git-novice/05-history/

see the third question at the bottom of the page.