Update SUMMARY.md

SUMMARY.md

@@ -50,6 +50,7 @@
 * [Memory management](mm/README.md)
     * [Memblock](mm/linux-mm-1.md)
     * [Fixmaps and ioremap](mm/linux-mm-2.md)
+    * [kmemcheck](mm/mm-3.md)
 * [SMP]()
 * [Concepts](Concepts/README.md)
     * [Per-CPU variables](Concepts/per-cpu.md)