fixed creating in

docs/creating-in.md

@@ -72,6 +72,12 @@ Once resolved, every creation command follows the destination kind.
 - Selecting an existing cel changes the destination from the lane to the symbol
   placed by that cel; subsequent symbols and shapes become children there.
 
+Double-clicking a lane creates an empty cel at the playhead; beginning a drawing
+creates a drawing cel there. These are the same lane-creation operation with
+different payloads. The pointer chooses the lane, never a second creation time.
+The resulting cel is selected, so it immediately becomes the preferred target:
+drawing again enters that cel's symbol instead of replacing it.
+
 Thus no separate "new cel" versus "add inside" mode is needed. Selecting the
 lane header says new cel; selecting a cel says add inside.