Update docs to clarify that split containers get a representation of their children in the decoration

docs/hacking-howto

@@ -629,8 +629,8 @@ unmapped if it should not be visible anymore. +WM_STATE+ will be set to
 +x_draw_decoration+ draws window decorations. It is run for every leaf
 container (representing an actual X11 window) and for every non-leaf container
 which is in a stacked/tabbed container (because stacked/tabbed containers
-display a window decoration for split containers, which at the moment just says
-"another container").
+display a window decoration for split containers, which consists of a representation
+of the child container's names.
 
 Then, parameters are collected to be able to determine whether this decoration
 drawing is actually necessary or was already done. This saves a substantial

docs/userguide

@@ -256,8 +256,9 @@ workspace node’s orientation will be changed to +vertical+. The terminal windo
 you moved down is directly attached to the workspace and appears on the bottom
 of the screen. A new (horizontal) container was created to accommodate the
 other two terminal windows. You will notice this when switching to tabbed mode
-(for example). You would end up having one tab called "another container" and
-the other one being the terminal window you moved down.
+(for example). You would end up having one tab with a representation of the split
+container (e.g., "H[urxvt firefox]") and the other one being the terminal window
+you moved down.
 
 [[configuring]]
 == Configuring i3