Update SUMMARY.md

SUMMARY.md

@@ -14,11 +14,9 @@
     * [Continue architecture-specific boot-time initializations]()
 * [Memory management](mm/README.md)
     * [Memblock](mm/linux-mm-1.md)
-* [Initial ram disk]()
-   * [initrd]()
 * [Concepts](Concepts/README.md)
     * [Per-CPU variables](Concepts/per-cpu.md)
-    * [Cpumasks]()
+    * [Cpumasks](Concepts/cpumask.md)
 * [Data Structures in the Linux Kernel](DataStructures/README.md)
     * [Doubly linked list](DataStructures/dlist.md)
 * [Theory](Theory/README.md)
@@ -26,6 +24,8 @@
     * [Elf64](Theory/ELF.md)
     * [CPUID]()
     * [MSR]()
+* [Initial ram disk]()
+   * [initrd]()
 * [Misc]()
     * [Kernel building and instalation]() 
     * [Write and Submit your first Linux kernel Patch]()