Describe the bug
Lists are introduced for the first time in the Expense Tracker project, but there's no mention that list elements can be referenced by their index, similarly to the characters in a string.

Expected behavior
We should add a brief explanation, possibly in step 2

Although this is not the purpose of this project, we could add a few steps to make campers familiarize with lists (indexing, appending/inserting elements, modifying an element etc.) in a similar way to what we have done with dictionaries in the Shortest Path Algorithm project starting from step 2 up to step 14.