Add nss-certs

We at least need nss-certs for running guix system reconfigure
manually, so it's a good idea to have it.

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>

mumble-vm-system.scm.tmpl

@@ -11,6 +11,7 @@
 (define-module (mumble-vm-system)
   #:use-module (gnu)
   #:use-module (gnu packages admin)
+  #:use-module (gnu packages certs)
   #:use-module (gnu packages dns)
   #:use-module (gnu packages linux)
   #:use-module (gnu packages ssh)
@@ -169,6 +170,7 @@ the services after that.")
            mumble-vm-config
            net-tools
            nmon
+           nss-certs
            openssh-sans-x
            website)
      (if enable-wireguard?