Document using HashMaps as function arguments #47
Description
New changes in https://github.com/extendr/extendr/pull/854/files allow us to use hash maps as function arguments for lists.
One thing to note is that if we have the same name multiple times in the list it will overwrite itself. eg list(x = 1, x = 2) the value in the hashmap will be ("x", 2).
Additionally we should give users a reminder that HashMaps are not ordered so we cannot expect the output from List::from_hashmap() to be in the same order.