Change timeout to string format in execute method

Updated timeout parameter in execute method to accept a string format for time duration.

Author: rmcdaniel

docs/features/signal+timer.md

@@ -23,8 +23,7 @@ class MyWorkflow extends Workflow
 
     public function execute()
     {
-        // Wait for 5 minutes or $ready = true, whichever comes first
-        $result = yield awaitWithTimeout(300, fn () => $this->ready);
+        $result = yield awaitWithTimeout('5 minutes', fn () => $this->ready);
     }
 }
 ```
@@ -36,5 +35,3 @@ $workflow->setReady();
 ```
 
 Or, if the specified timeout is reached, the workflow will continue without the signal. The return value is `true` if the signal was received before the timeout, or `false` if the timeout was reached without receiving the signal.
-
-You may also specify the time to wait as a string e.g. '30 seconds', '5 minutes' or '2 weeks'.