Documentation for extra input signals

Readme.md

@@ -76,6 +76,17 @@ expected. All other characters are ignored.
 Writing an own class for player input should be fairly easy. Within its own
 thread the class can do whatever it wants (including blocking I/O). When it
 wants to signal a button was pressed it just needs to emit a ButtonEvent.
+An input class has two functions which are called while a question is on
+display:
+
+ - `buzzersOpen(isOpen)` is called, when the question is first displayed,
+    when the question is reopened after a false answer and when the question is
+	closed after either a correct answer or no answer at all.
+
+ - `playerGotQuestion(playerNo)` is called, whenever a player pressed
+    their button *and* got the turn to answer. Note that no extra
+	buzzers-are-closed (`buzzersOpen(False)`) event is sent, when a button
+	is pressed.
 
 
 Known Bugs