documentation: add links to SELinux resources

Add links to the SELinux kernel subsystem README.md file, the
SELinux kernel wiki, and the SELinux userspace wiki to the
SELinux guide.

Signed-off-by: Stephen Smalley <stephen.smalley.work@gmail.com>
[PM: spacing and style corrections, subject tweak]
Signed-off-by: Paul Moore <paul@paul-moore.com>

Author: stephensmalley

Documentation/admin-guide/LSM/SELinux.rst

@@ -2,6 +2,17 @@
 SELinux
 =======
 
+Information about the SELinux kernel subsystem can be found at the
+following links:
+
+	https://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/selinux.git/tree/README.md
+
+	https://github.com/selinuxproject/selinux-kernel/wiki
+
+Information about the SELinux userspace can be found at:
+
+	https://github.com/SELinuxProject/selinux/wiki
+
 If you want to use SELinux, chances are you will want
 to use the distro-provided policies, or install the
 latest reference policy release from