doc [completion]: add a doc comment

GitOrigin-RevId: a2bea8b494d2190f003bf3a151294ca741604505

platform/lang-impl/src/com/intellij/codeInsight/lookup/impl/LookupImpl.java

@@ -264,6 +264,10 @@ public class LookupImpl extends LightweightHint implements LookupEx, Disposable,
     }
   }
 
+  /**
+   * let LookupImpl know that user changed selected element
+   * @see #isSelectionTouched()
+   */
   public void markSelectionTouched() {
     if (!ApplicationManager.getApplication().isUnitTestMode()) {
       ThreadingAssertions.assertEventDispatchThread();