Describe the Select node

Behaviors.md

@@ -114,6 +114,8 @@ shown on the node and editable in the inspector.
   list, or a struct whose fields are all empty such as a position (0, 0), so a real 0 or false on a
   is passed over; *Nothing there* keeps 0 and false and falls back only on nothing, an empty text or
   an empty list; *Only a missing value* falls back only where nothing arrives at all),
+  `Select` (`true` if the condition holds, else `false` — the same action with one of two values,
+  such as a walk or an idle animation for one `Play animation`; `Branch` is for two different actions),
   lists `List` (a constant), `Fill` (one value repeated — how an empty board is made), `Count`,
   `Item at`, `Set item` (a *new* list, the one that came in is left alone), `Sub list`,
   `Join lists`, `Index of` (by identity where the items are objects), structs `Pack`/`Expand`,
@@ -151,7 +153,7 @@ shown on the node and editable in the inspector.
   undo.
 - **Ports that carry one and the same value** say so with `sharedType` (`{inputs, outputs}`), and
   their outputs then take the type of what is plugged in: with `a` and `b` of a `First not empty`
-  both fed by a number, `value` is a number port — coloured as one, and only accepted where a
+  (or `false` and `true` of a `Select`) both fed by a number, `value` is a number port — coloured as one, and only accepted where a
   number fits. The inputs stay `any`: they take everything, so a connected one can be swapped for
   another type without unplugging it first — their **pin is still painted** as whatever flows in,
   each one on its own, so a pair fed by a number and a text shows two colours and thereby says why