Clarify determinism of wait_condition with comment (#1638)

* Clarify determinism of wait_condition with comment

* Make 0 make more sense

Author: Sushisource

temporalio/workflow/_context.py

@@ -928,6 +928,11 @@ async def wait_condition(
     This function returns when the callback returns true (invoked each loop
     iteration) or the timeout has been reached.
 
+    Importantly, using `None` value for ``timeout`` means that no Temporal timer is created. This
+    means changing from `None` to a positive value (or the inverse) constitutes a nondeterministic
+    change to workflow code. Using ``0`` will cause this function to immediately throw a timeout and
+    should not be used.
+
     Args:
         fn: Non-async callback that accepts no parameters and returns a boolean.
         timeout: Optional number of seconds to wait until throwing