Update SUMMARY.md

SUMMARY.md

@@ -10,7 +10,7 @@
     * [First steps in the kernel](Initialization/linux-initialization-1.md)
     * [Early interrupts handler](Initialization/linux-initialization-2.md)
     * [Last preparations before the kernel entry point](Initialization/linux-initialization-3.md)
-    * [Kernel entry point]()
+    * [Kernel entry point](Initialization/linux-initialization-4.md)
     * [Continue architecture-specific boot-time initializations]()
 * [Memory management](mm/README.md)
     * [Memblock](mm/linux-mm-1.md)