selinux: runtime disable is deprecated, add some ssleep() discomfort

We deprecated the SELinux runtime disable functionality in Linux
v5.6, and it is time to get a bit more serious about removing it.
Add a five second sleep to anyone using it to help draw their
attention to the deprecation and provide a URL which helps explain
things in more detail, including how to add kernel command line
parameters to some of the more popular Linux distributions.

Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>