Add doc section to explain how to use DebugTimer for custom profiling

Author: Neluxx

docs/en/index.rst

@@ -323,6 +323,22 @@ Helper Functions
 * ``sql()`` Dumps out the SQL from an ORM query.
 * ``sqld()`` Dumps out the SQL from an ORM query, and exits.
 
+Using DebugTimer
+----------------
+
+Use the DebugTimer to measure parts of the code that are not captured by the default timers, such as portions of a controller action, service logic or view rendering::
+
+    use DebugKit\DebugTimer;
+
+    public function view($id)
+    {
+        DebugTimer::start('load_article', 'Fetching article from database');
+            ...
+        DebugTimer::stop('load_article');
+    }
+
+When that request finishes, the Timer panel will include the custom timers.
+
 Tracing query execution
 =======================