clarify stream bulk insert (phoenixframework#3023)

lib/phoenix_live_view.ex

@@ -1532,6 +1532,19 @@ defmodule Phoenix.LiveView do
       collection on the client. By default `-1` is used, which appends the items
       to the parent DOM container. A value of `0` prepends the items.
 
+      Note that this operation is equal to inserting the items one by one, each at
+      the given index. Therefore, when inserting multiple items at an index other than `-1`,
+      the UI will display the items in reverse order:
+
+          stream(socket, :songs, [song1, song2, song3], at: 0])
+
+      In this case the UI will prepend `song1`, then `song2` and then `song3`, so it will show
+      `song3`, `song2`, `song1` and then any previously inserted items.
+
+      To insert in the order of the list, use `Enum.reverse/1`:
+
+          stream(socket, :songs, Enum.reverse([song1, song2, song3]), at: 0])
+
     * `:reset` - the boolean to reset the stream on the client or not. Defaults
       to `false`.