Add issue templates and a user support page

This will hopefully help directing our users to better user support
resources as well as give some relevant advice in issue templates.

https://help.github.com/articles/setting-up-your-project-for-healthy-contributions/



Reviewed-by: Nicola Tuveri <nic.tuv@gmail.com>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/7623)