examples: long_wait py_func/lua_func to exercise Stop

Two extra steps in example_simple.tum that sleep for 10s, used to
verify that pressing Stop interrupts engaged blocking steps.

doc/examples/lua_func.lua

@@ -1,4 +1,5 @@
 tm = require("tm")
+socket = require("socket")
 
 local module = {}
 
@@ -7,4 +8,8 @@ function module.func_to_be_executed(param)
     return param
 end
 
+function module.long_wait(sec)
+    socket.sleep(sec)
+end
+
 return module