php: Recommend calling flush for long running CLI tasks (#14468)

Author: cleptric

platform-includes/logs/usage/php.mdx

@@ -17,3 +17,6 @@ You can pass additional attributes directly to the logging functions. These prop
 // Somewhere at the end of your execution, you should flush the logger to send pending logs to Sentry.
 \Sentry\logger()->flush();
 ```
+
+If you are using logs in long running CLI tasks, we recommend periodically calling `\Sentry\logger()->flush()` to keep memory pressure low and avoid any logs being discarded to due size-limits.
+