edit to do list

todo.md

@@ -1,6 +1,6 @@
 ## Other
 
-- when click another marker, it should close the other one.
+- when click another marker, it should close the other one (use either useContext/create context for this or useState, or Redux([guide here](https://egghead.io/courses/fundamentals-of-redux-course-from-dan-abramov-bd5cc867))).
 - edit readme so other people can use/edit. Write contributing.md maybe.
 - More info links for the buildings - there are some really good websites out there about these buildings which I'd like to signpost to users of the map.
 - check google search position on oct 21 or later (maybe use google search console) and improve SEO as needed.