Add seccomp tutorial to index

This adds the seccomp tutorial page to the index side by side to
AppArmor.

Signed-off-by: Sascha Grunert <sgrunert@redhat.com>

content/en/docs/tutorials/_index.md

@@ -51,6 +51,8 @@ Before walking through each tutorial, you may want to bookmark the
 
 * [AppArmor](/docs/tutorials/clusters/apparmor/)
 
+* [seccomp](/docs/tutorials/clusters/seccomp/)
+
 ## Services
 
 * [Using Source IP](/docs/tutorials/services/source-ip/)