Merge pull request #4759 from alexanderkjeldaas/do-not-break-grsecurity

Document likely breakage when people update the kernel.

pkgs/os-specific/linux/kernel/linux-3.14.nix

@@ -1,6 +1,7 @@
 { stdenv, fetchurl, ... } @ args:
 
 import ./generic.nix (args // rec {
+  # Remember to update grsecurity!
   version = "3.14.23";
   extraMeta.branch = "3.14";
 

pkgs/os-specific/linux/kernel/linux-3.17.nix

@@ -1,6 +1,7 @@
 { stdenv, fetchurl, ... } @ args:
 
 import ./generic.nix (args // rec {
+  # Remember to update grsecurity!
   version = "3.17.2";
   extraMeta.branch = "3.17";