Minor. Add a comment to KtLightElement::givenAnnotations

compiler/light-classes/src/org/jetbrains/kotlin/asJava/elements/KtLightElements.kt

@@ -27,6 +27,12 @@ import org.jetbrains.kotlin.resolve.jvm.diagnostics.JvmDeclarationOriginKind
 interface KtLightElement<out T : KtElement, out D : PsiElement> : PsiElement {
     val kotlinOrigin: T?
 
+    /**
+     * KtLightModifierList by default retrieves annotation from the relevant KtElement or from clsDelegate
+     * But we have none of them for KtUltraLightAnnotationForDescriptor built upon descriptor
+     * For that case, KtLightModifierList in the beginning checks `givenAnnotations` and uses them if it's not null
+     * Probably, it's a bit dirty solution. But, for now it's not clear how to make it better
+     */
     val givenAnnotations: List<KtLightAbstractAnnotation>? get() = null
 
     val clsDelegate: D