SUMMARY updated

SUMMARY.md

@@ -3,3 +3,5 @@
 * [Booting](Booting/README.md)
     * [From bootloader to kernel](Booting/linux-bootstrap-1.md)
     * [First steps in the kernel setup code](Booting/linux-bootstrap-1.md)
+* [Useful links](LINKS.md)
+* [Contributors](contributors.md)