Add encouraging message at the end of M1

[ArturoAmorQ]

As discussed in this forum post, we can improve the friendliness of the MOOC by adding a short encouraging message somewhere at the end of the first Module. Maybe after the first wrap-up quiz.

The message proposed by @ogrisel is:

It is normal for this module to take longer than expected for people who have little experience in Python programming, but don't get discouraged! The programming mechanisms will come with experience and the programming exercises in the following modules will seem more and more natural as time goes by.