MIB training slides - add info about template document

["Wijnen, Bert (Bert)" <bwijnen@lucent.com>]

Dave Harrington suggested to add the MIB template document
to the training slides. I saw that too late (too much email
to handle in the 1 day between nmy vacation and IETF).

I will add it, so it will be there if the slides are
re-used in the future.

more suggestions are of course welcome.

Bert