Update SUMMARY.md

SUMMARY.md

@@ -10,8 +10,8 @@
     * [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)
-* [Memory management](MM/README.md)
-    * [Memblock](MM/linux-mm-1.md)
+* [Memory management](mm/README.md)
+    * [Memblock](mm/linux-mm-1.md)
 * [Data Structures in the Linux Kernel](DataStructures/README.md)
     * [Doubly linked list](DataStructures/dlist.md)
 * [Theory](Theory/README.md)