Add Donate button + reasoning to end of directions

[tedspare]

• After the final mural step in directions, nudge the user to donate
• Use language along the lines of "If you enjoyed this tour, we invite you to become a supporter! MU MTL is a Montreal-based not-for-profit. Donations go toward covering our server costs and time." Research best practices for donation language. These can easily get annoying, like Wikipedia's. Leverage pride rather than guilt! 🙌