Document more shortcuts

I'm probably missing some still

docs/shortcuts.md

@@ -6,6 +6,8 @@ The modifier is <kbd>Ctrl</kbd> on Windows & Linux and <kbd>⌘</kbd> on Mac.
 - <kbd>Ctrl</kbd>/<kbd>⌘</kbd>+<kbd>d</kbd> - toggle mic mute
 - <kbd>Ctrl</kbd>/<kbd>⌘</kbd>+<kbd>e</kbd> - toggle video on/off
 - <kbd>Ctrl</kbd>/<kbd>⌘</kbd>+<kbd>k</kbd> - jump to named room
-- <kbd>↑</kbd>/<kbd>↓</kbd> - navigate within room list
+- <kbd>↑</kbd>/<kbd>↓</kbd> - navigate old messages to edit in composer
+- <kbd>↑</kbd>/<kbd>↓</kbd> - next/prev room when focus in room list
+- <kbd>Alt</kbd>+<kbd>↑</kbd>/<kbd>↓</kbd> - scroll timeline up/down ?
 - <kbd>PageUp</kbd>/<kbd>PageDown</kbd> - scroll timeline up/down
 - <kbd>Ctrl</kbd>/<kbd>⌘</kbd>+<kbd>Home</kbd>/<kbd>End</kbd> - jump to timeline start/end