Usage:
$ python3 main.py
Application first displays a word in Swahili
After 4 seconds, the card flips, showing its translation in English
The user can then either select the green or red button.
If the user knows the word, select the green button, and another word will be shown.
If the user doesn't know the word, select the red button, which adds it to a list of words to be learnt and another word is shown.