Update SUMMARY.md

SUMMARY.md

@@ -12,15 +12,15 @@
     * [Last preparations before the kernel entry point](Initialization/linux-initialization-3.md)
     * [Kernel entry point]()
     * [Continue architecture-specific boot-time initializations]()
-* [Initial ram disk]()
-   * [initrd]()
 * [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)
+* [Initial ram disk]()
+   * [initrd]()
 * [Concepts](Concepts/README.md)
     * [Per-CPU variables](Concepts/per-cpu.md)
     * [Cpumasks]()
+* [Data Structures in the Linux Kernel](DataStructures/README.md)
+    * [Doubly linked list](DataStructures/dlist.md)
 * [Theory](Theory/README.md)
     * [Paging](Theory/Paging.md)
     * [Elf64](Theory/ELF.md)