2. As a user, I want to be able to navigate between the “list” view and the “add an item” view

[stacietaylorcima]

This is 1 of 2 stories that should be completed in the first week to enable further development of the app.

AC:

• react-router-dom has been added as a project dependency
• 2 tabs are present and persistent at the bottom of the app: one for the “list” view, the other for the “add an item” view
• Whichever tab is selected should indicate somehow that it is selected
• When a link is clicked, the browser URL updates to represent the current view