Update SUMMARY.md

SUMMARY.md

@@ -21,7 +21,7 @@
     * [Introduction](interrupts/interrupts-1.md)
     * [Start to dive into interrupts](interrupts/interrupts-2.md)
     * [Interrupt handlers](interrupts/interrupts-3.md)
-    * [Initialization of non-early interrupt gates]()
+    * [Initialization of non-early interrupt gates](interrupts/interrupts-4.md)
 * [Memory management](mm/README.md)
     * [Memblock](mm/linux-mm-1.md)
     * [Fixmaps and ioremap](mm/linux-mm-2.md)