Fix typo in side-effects documentation

Author: rmcdaniel

docs/features/side-effects.md

@@ -29,7 +29,7 @@ The workflow will only call `random_int()` once and save the result, even if the
 
 Signals are applied before the workflow continues execution. That means a signal-mutated variable can break replays unless the control flow decision is recorded deterministically.
 
-Use `sideEffect` to snapshot any signal-driven branch decision:
+Use `sideEffect()` to snapshot any signal-driven branch decision:
 
 ```php
 use function Workflow\{activity, sideEffect};