Added issue template

Created by: Silabs-ArjanB

Hi @davideschiavone

This pull request is for an 'issue template' similar to the one in core-v-verif/.github/ISSUE_TEMPLATE

I did not have a way to check whether this pull request actually works or not. Could you please check if the added files are sound?

Signed-off-by: Arjan Bink Arjan.Bink@silabs.com