write how to use the stopwatch in symfony profiler

Author: SimonHeimberg

components/stopwatch.rst

@@ -48,6 +48,18 @@ You can also provide a category name to an event::
 You can consider categories as a way of tagging events. For example, the
 Symfony Profiler tool uses categories to nicely color-code different events.
 
+Usage in symfony
+----------------
+
+In a Controller, do:
+
+    $stopwatch = $this->get('debug.stopwatch');
+    $stopwatch->start('anEvent');
+
+Or inject `Symfony\Component\Stopwatch\Stopwatch` by autowiring.
+
+Thereafter this timing can be seen in the profiler.
+
 Periods
 -------