Add *.snk strong name key files (#2483)

* Add *.snk strong name key files

Strong name key files shouldn't be included in a repository AFAIK. they are intended to sign build output to verify that it comes from the correct publisher. having an *.snk in a repository would allow anyone to produce build as if they were the original publisher.

I guess some OSS projects might like to have *.snk files in their repos but that would be an exception to the rule.

* Make use of *.snk optional

Add note explaining use.

* Reduce explanation

Just use a link instead