Add PickANumber example

examples/src/main/viaduct/synchronization/PickANumber.via

@@ -0,0 +1,16 @@
+host alice : {A}
+host bob   : {B & A<-}
+
+fun main() {
+    let $pick = input int from alice;
+    let $trusted_pick = endorse $pick from {A};
+
+    let $guess = input int from bob;
+    let $revealed_guess = declassify $guess to {A ⊓ B};
+
+    let $revealed_pick = declassify $trusted_pick to {A ⊓ B};
+    let $bob_wins = $revealed_pick == $revealed_guess;
+
+    output $bob_wins to alice;
+    output $bob_wins to bob;
+}